Handover random access

ABSTRACT

Systems, apparatuses, and methods are described for wireless communications. Random access procedures may include various types of procedures, such as 4-step or 2-step random access procedures. One or more indicators may be included in one or more messages for a handover to indicate a type of a random access procedure.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of co-pending U.S. applicationSer. No. 15/933,301, titled “Handover Random Access,” filed on Mar. 22,2018, which claims the benefit of U.S. Provisional Application No.62/475,033, titled “Handover Random Access,” filed on Mar. 22, 2017,both of which are hereby incorporated by reference in their entireties.

BACKGROUND

In wireless communications, such as between a wireless device and a basestation, a random access (RA) procedure may be performed to initiate thecommunications. A wireless device may handover from a source basestation to a target base station, e.g., if the wireless device movesfrom a location in a first cell served by the source base station to alocation in a second cell served by the target base station. The sourcebase station and the target base station may perform different RAprocedures to initiate communications with wireless devices.Difficulties may arise in determining a type of RA procedure to performwhen a handover occurs.

SUMMARY

The following summary presents a simplified summary of certain features.The summary is not an extensive overview and is not intended to identifykey or critical elements.

Systems, apparatuses, and methods are described for determining a typeof RA procedure to perform when a handover occurs. RA procedures maycomprise different steps. For example, a two-step RA procedure or afour-step RA procedure may be performed. The type of RA procedure may beidentified by one or more indicators. The one or more indicators may beincluded in messages sent to or from devices involved in a handover,such as a wireless device, a source base station, a target base station,and/or one or more core network devices.

These and other features and advantages are described in greater detailbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

Some features are shown by way of example, and not by limitation, in theaccompanying drawings. In the drawings, like numerals reference similarelements.

FIG. 1 shows example sets of orthogonal frequency division multiplexing(OFDM) subcarriers.

FIG. 2 shows example transmission time and reception time for twocarriers in a carrier group.

FIG. 3 shows example OFDM radio resources.

FIG. 4 shows hardware elements of a base station and a wireless device.

FIG. 5A, FIG. 5B, FIG. 5C and FIG. 5D show examples for uplink anddownlink signal transmission.

FIG. 6 shows an example protocol structure with multi-connectivity.

FIG. 7 shows an example protocol structure with carrier aggregation (CA)and dual connectivity (DC).

FIG. 8 shows example timing advance group (TAG) configurations.

FIG. 9 shows example message flow in a random access process in asecondary TAG.

FIG. 10A and FIG. 10B show examples for interfaces between a 5G corenetwork and base stations.

FIG. 11A, FIG. 11B, FIG. 11C, FIG. 11D, FIG. 11E, and FIG. 11F showexamples for architectures of tight interworking between 5G RAN and longterm evolution (LTE) radio access network (RAN).

FIG. 12A, FIG. 12B, and FIG. 12C show examples for radio protocolstructures of tight interworking bearers.

FIG. 13A and FIG. 13B show examples for gNodeB (gNB) deploymentscenarios.

FIG. 14 functional split option examples of a centralized gNB deploymentscenario.

FIG. 15 shows examples of contention-based and contention free randomaccess procedures.

FIG. 16 shows an example of a random access preamble selectionprocedure.

FIG. 17 shows an example media access control (MAC) packet data unit(PDU) format of an example of MAC PDU comprising a MAC header and MACrandom access responses (RARs) for a four-step RA procedure.

FIG. 18 shows an example of shows an example of an uplink resource for atransmission in a first step of a two-step RA procedure.

FIG. 19 shows an example MAC RAR format of an example of MAC RARcomprising a timing advance command, Uplink (UL) Grant, and TemporaryCell-Radio Network Temporary Identifier for a four-step RA procedure.

FIG. 20 shows an example of a two-step RA procedure.

FIG. 21 shows an example of contention resolution for a two-step RAprocedure.

FIG. 22 shows an example of a two-step RA procedure of an examplefailure of UL transmission for n times.

FIG. 23 shows example RARs with a fixed size 8 bytes for example RARformats for two-step RA procedures and for a four-step RA procedure.

FIG. 24 shows an example RAR with a fixed size 12 bytes for example RARformats for two-step and four-step RA procedures.

FIG. 25 shows an example for hybrid automatic repeat request (HARQ)retransmission, such as when a cell detects a random access preambleidentifier but fails to decode data.

FIG. 26 shows an example of a two-step RA procedure failure as thenumber of HARQ retransmission reaches a threshold.

FIG. 27 shows an example of a two-step RA procedure when a base stationdecodes a RAP and UL data and responds with an RAR to a wireless device.

FIG. 28 shows an example of a handover of a wireless device from asource base station to a target base station.

FIG. 29 shows an example of a handover of a wireless device from asource base station to a target base station that is facilitated by acore network entity.

FIG. 30 shows an example of handover procedures for a wireless device.

FIG. 31 shows an example of handover procedures for a source basestation.

FIG. 32 shows an example of handover procedures for a target basestation.

FIG. 33 shows an example of handover procedures for a core networkdevice.

FIG. 34 shows an example of handover procedures with different types ofRA procedures for a wireless device.

DETAILED DESCRIPTION

The accompanying drawings, which form a part hereof, show examples ofthe disclosure.

It is to be understood that the examples shown in the drawings and/ordiscussed herein are non-exclusive and that there are other examples ofhow the disclosure may be practiced.

Examples may enable operation of carrier aggregation and may be employedin the technical field of multicarrier communication systems. Examplesmay relate to signal timing in a multicarrier communication systems.

The following Acronyms are used throughout the present disclosure:

3GPP 3rd Generation Partnership Project

5G 5th generation wireless systems

5GC 5G Core Network

ACK Acknowledgement

AMF Access and Mobility Management Function

ASIC application-specific integrated circuit

BPSK binary phase shift keying

CA carrier aggregation

CC component carrier

CDMA code division multiple access

CP cyclic prefix

CPLD complex programmable logic devices

CSI channel state information

CSS common search space

CU central unit

DC dual connectivity

DCI downlink control information

DFTS-OFDM discrete fourier transform spreading OFDM

DL downlink

DU distributed unit

eLTE enhanced LTE

eMBB enhanced mobile broadband

eNB evolved Node B

EPC evolved packet core

E-UTRAN evolved-universal terrestrial radio access network

FDD frequency division multiplexing

FPGA field programmable gate arrays

Fs-C Fs-control plane

Fs-U Fs-user plane

gNB next generation node B

HARQ hybrid automatic repeat request

HDL hardware description languages

ID identifier

IE information element

LTE long term evolution

MAC media access control

MCG master cell group

MeNB master evolved node B

MIB master information block

MME mobility management entity

mMTC massive machine type communications

NACK Negative Acknowledgement

NAS non-access stratum

NG CP next generation control plane core

NGC next generation core

NG-C NG-control plane

NG-U NG-user plane

NR MAC new radio MAC

NR PDCP new radio PDCP

NR PHY new radio physical

NR RLC new radio RLC

NR RRC new radio RRC

NR new radio

NR new radio

NSSAI network slice selection assistance information

OFDM orthogonal frequency division multiplexing

PCC primary component carrier

PCell primary cell

PDCCH physical downlink control channel

PDCP packet data convergence protocol

PDU packet data unit

PHICH physical HARQ indicator channel

PHY physical

PLMN public land mobile network

PSCell primary secondary cell

pTAG primary timing advance group

PUCCH physical uplink control channel

PUSCH physical uplink shared channel

QAM quadrature amplitude modulation

QPSK quadrature phase shift keying

RA random access

RACH random access channel

RAN radio access network

RAP random access preamble

RAPID/RAP ID random access preamble identifier

RAR random access response

RB resource blocks

RBG resource block groups

RLC radio link control

RRC radio resource control

RRM radio resource management

RV redundancy version

SCC secondary component carrier

SCell secondary cell

SCG secondary cell group

SC-OFDM single carrier-OFDM

SDU service data unit

SeNB secondary evolved node B

SFN system frame number

S-GW serving gateway

SIB system information block

SC-OFDM single carrier orthogonal frequency division multiplexing

SRB signaling radio bearer

sTAG(s) secondary timing advance group(s)

TA timing advance

TAG timing advance group

TAI tracking area identifier

TAT time alignment timer

TDD time division duplexing

TDMA time division multiple access

TTI transmission time interval

TB transport block

UE user equipment

UL uplink

UPGW user plane gateway

URLLC ultra-reliable low-latency communications

VHDL VHSIC hardware description language

Xn-C Xn-control plane

Xn-U Xn-user plane

Xx-C Xx-control plane

Xx-U Xx-user plane

Examples may be implemented using various physical layer modulation andtransmission mechanisms. Example transmission mechanisms may include,but are not limited to: CDMA, OFDM, TDMA, Wavelet technologies, and/orthe like. Hybrid transmission mechanisms such as TDMA/CDMA, andOFDM/CDMA may also be employed. Various modulation schemes may beapplied for signal transmission in the physical layer. Examples ofmodulation schemes include, but are not limited to: phase, amplitude,code, a combination of these, and/or the like. An example radiotransmission method may implement QAM using BPSK, QPSK, 16-QAM, 64-QAM,256-QAM, and/or the like. Physical radio transmission may be enhanced bydynamically or semi-dynamically changing the modulation and codingscheme depending on transmission requirements and radio conditions.

FIG. 1 shows example sets of OFDM subcarriers. As shown in this example,arrow(s) in the diagram may depict a subcarrier in a multicarrier OFDMsystem. The OFDM system may use technology such as OFDM technology,DFTS-OFDM, SC-OFDM technology, or the like. For example, arrow 101 showsa subcarrier transmitting information symbols. FIG. 1 is shown as anexample, and a typical multicarrier OFDM system may include moresubcarriers in a carrier. For example, the number of subcarriers in acarrier may be in the range of 10 to 10,000 subcarriers. FIG. 1 showstwo guard bands 106 and 107 in a transmission band. As shown in FIG. 1,guard band 106 is between subcarriers 103 and subcarriers 104. Theexample set of subcarriers A 102 includes subcarriers 103 andsubcarriers 104. FIG. 1 also shows an example set of subcarriers B 105.As shown, there is no guard band between any two subcarriers in theexample set of subcarriers B 105. Carriers in a multicarrier OFDMcommunication system may be contiguous carriers, non-contiguouscarriers, or a combination of both contiguous and non-contiguouscarriers.

FIG. 2 shows an example with transmission time and reception time fortwo carriers. A multicarrier OFDM communication system may include oneor more carriers, for example, ranging from 1 to 10 carriers. Carrier A204 and carrier B 205 may have the same or different timing structures.Although FIG. 2 shows two synchronized carriers, carrier A 204 andcarrier B 205 may or may not be synchronized with each other. Differentradio frame structures may be supported for FDD and TDD duplexmechanisms. FIG. 2 shows an example FDD frame timing. Downlink anduplink transmissions may be organized into radio frames 201. In thisexample, radio frame duration is 10 milliseconds (msec). Other framedurations, for example, in the range of 1 to 100 msec may also besupported. In this example, each 10 msec radio frame 201 may be dividedinto ten equally sized subframes 202. Other subframe durations such asincluding 0.5 msec, 1 msec, 2 msec, and 5 msec may also be supported.Subframe(s) may consist of two or more slots (e.g., slots 206 and 207).For the example of FDD, 10 subframes may be available for downlinktransmission and 10 subframes may be available for uplink transmissionsin each 10 msec interval. Uplink and downlink transmissions may beseparated in the frequency domain. A slot may be 7 or 14 OFDM symbolsfor the same subcarrier spacing of up to 60 kHz with normal CP. A slotmay be 14 OFDM symbols for the same subcarrier spacing higher than 60kHz with normal CP. A slot may contain all downlink, all uplink, or adownlink part and an uplink part, and/or alike. Slot aggregation may besupported, e.g., data transmission may be scheduled to span one ormultiple slots. In an example, a mini-slot may start at an OFDM symbolin a subframe. A mini-slot may have a duration of one or more OFDMsymbols. Slot(s) may include a plurality of OFDM symbols 203. The numberof OFDM symbols 203 in a slot 206 may depend on the cyclic prefix lengthand subcarrier spacing.

FIG. 3 shows an example of OFDM radio resources. The resource gridstructure in time 304 and frequency 305 is shown in FIG. 3. The quantityof downlink subcarriers or RBs may depend, at least in part, on thedownlink transmission bandwidth 306 configured in the cell. The smallestradio resource unit may be called a resource element (e.g., 301).Resource elements may be grouped into resource blocks (e.g., 302).Resource blocks may be grouped into larger radio resources calledResource Block Groups (RBG) (e.g., 303). The transmitted signal in slot206 may be described by one or several resource grids of a plurality ofsubcarriers and a plurality of OFDM symbols. Resource blocks may be usedto describe the mapping of certain physical channels to resourceelements. Other pre-defined groupings of physical resource elements maybe implemented in the system depending on the radio technology. Forexample, 24 subcarriers may be grouped as a radio block for a durationof 5 msec. A resource block may correspond to one slot in the timedomain and 180 kHz in the frequency domain (for 15 kHz subcarrierbandwidth and 12 subcarriers).

Multiple numerologies may be supported. A numerology may be derived byscaling a basic subcarrier spacing by an integer N. Scalable numerologymay allow at least from 15 kHz to 480 kHz subcarrier spacing. Thenumerology with 15 kHz and scaled numerology with different subcarrierspacing with the same CP overhead may align at a symbol boundary every 1msec in a NR carrier.

FIG. 4 shows hardware elements of a base station 401 and a wirelessdevice 406. A communication network 400 may include at least one basestation 401 and at least one wireless device 406. The base station 401may include at least one communication interface 402, one or moreprocessors 403, and at least one set of program code instructions 405stored in non-transitory memory 404 and executable by the one or moreprocessors 403. The wireless device 406 may include at least onecommunication interface 407, one or more processors 408, and at leastone set of program code instructions 410 stored in non-transitory memory409 and executable by the one or more processors 408. A communicationinterface 402 in the base station 401 may be configured to engage incommunication with a communication interface 407 in the wireless device406, such as via a communication path that includes at least onewireless link 411. The wireless link 411 may be a bi-directional link.The communication interface 407 in the wireless device 406 may also beconfigured to engage in communication with the communication interface402 in the base station 401. The base station 401 and the wirelessdevice 406 may be configured to send and receive data over the wirelesslink 411 using multiple frequency carriers. Base stations, wirelessdevices, and other communication devices may include structure andoperations of transceiver(s). A transceiver is a device that includesboth a transmitter and receiver. Transceivers may be employed in devicessuch as wireless devices, base stations, relay nodes, and/or the like.Examples for radio technology implemented in the communicationinterfaces 402, 407 and the wireless link 411 are shown in FIG. 1, FIG.2, FIG. 3, FIG. 5, and associated text. The communication network 400may comprise any number and/or type of devices, such as, for example,wireless devices, mobile devices, handsets, tablets, laptops, internetof things (IoT) devices, hotspots, cellular repeaters, computingdevices, and/or, more generally, user equipment (e.g., UE). Although oneor more of the above types of devices may be referenced herein (e.g.,UE, wireless device, etc.), it should be understood that any deviceherein may comprise any one or more of the above types of devices orsimilar devices. The communication network 400, and any other networkreferenced herein, may comprise an LTE network, a 5G network, or anyother network for wireless communications. Apparatuses, systems, and/ormethods described herein may generally be described as implemented onone or more devices (e.g., wireless device, base station, eNB, gNB,computing device, etc.), in one or more networks, but it will beunderstood that one or more features and steps may be implemented on anydevice and/or in any network. As an example, any reference to a basestation may comprise an eNB, a gNB, a computing device, or any otherdevice, and any reference to a wireless device may comprise a UE, ahandset, a mobile device, a computing device or any other device.

The communications network 400 may comprise Radio Access Network (RAN)architecture. The RAN architecture may comprise one or more RAN nodesthat may be a next generation Node B (gNB) (e.g., 401) providing NewRadio (NR) user plane and control plane protocol terminations towards afirst wireless device (e.g. 406). A RAN node may be a next generationevolved Node B (ng-eNB), providing Evolved UMTS Terrestrial Radio Access(E-UTRA) user plane and control plane protocol terminations towards asecond wireless device. The first wireless device may communicate with agNB over a Uu interface. The second wireless device may communicate witha ng-eNB over a Uu interface. Base station 401 may comprise at least oneof a gNB, ng-eNB, and or the like.

A gNB or an ng-eNB may host functions such as: radio resource managementand scheduling, IP header compression, encryption and integrityprotection of data, selection of Access and Mobility Management Function(AMF) at User Equipment (UE) attachment, routing of user plane andcontrol plane data, connection setup and release, scheduling andtransmission of paging messages (originated from the AMF), schedulingand transmission of system broadcast information (originated from theAMF or Operation and Maintenance (O&M)), measurement and measurementreporting configuration, transport level packet marking in the uplink,session management, support of network slicing, Quality of Service (QoS)flow management and mapping to data radio bearers, support of UEs inRRC_INACTIVE state, distribution function for Non-Access Stratum (NAS)messages, RAN sharing, and dual connectivity or tight interworkingbetween NR and E-UTRA.

One or more gNBs and/or one or more ng-eNBs may be interconnected witheach other by means of Xn interface. A gNB or an ng-eNB may be connectedby means of NG interfaces to 5G Core Network (5GC). 5GC may comprise oneor more AMF/User Plan Function (UPF) functions. A gNB or an ng-eNB maybe connected to a UPF by means of an NG-User plane (NG-U) interface. TheNG-U interface may provide delivery (e.g. non-guaranteed delivery) ofuser plane Protocol Data Units (PDUs) between a RAN node and the UPF. AgNB or an ng-eNB may be connected to an AMF by means of an NG-Controlplane (NG-C) interface. The NG-C interface may provide functions such asNG interface management, UE context management, UE mobility management,transport of NAS messages, paging, PDU session management, configurationtransfer or warning message transmission.

A UPF may host functions such as anchor point for intra-/inter-RadioAccess Technology (RAT) mobility (when applicable), external PDU sessionpoint of interconnect to data network, packet routing and forwarding,packet inspection and user plane part of policy rule enforcement,traffic usage reporting, uplink classifier to support routing trafficflows to a data network, branching point to support multi-homed PDUsession, QoS handling for user plane, e.g. packet filtering, gating,Uplink (UL)/Downlink (DL) rate enforcement, uplink traffic verification(e.g. Service Data Flow (SDF) to QoS flow mapping), downlink packetbuffering and/or downlink data notification triggering.

An AMF may host functions such as NAS signaling termination, NASsignaling security, Access Stratum (AS) security control, inter CoreNetwork (CN) node signaling for mobility between 3rd GenerationPartnership Project (3GPP) access networks, idle mode UE reachability(e.g., control and execution of paging retransmission), registrationarea management, support of intra-system and inter-system mobility,access authentication, access authorization including check of roamingrights, mobility management control (subscription and policies), supportof network slicing and/or Session Management Function (SMF) selection

An interface may be a hardware interface, a firmware interface, asoftware interface, and/or a combination thereof. The hardware interfacemay include connectors, wires, electronic devices such as drivers,amplifiers, and/or the like. A software interface may include codestored in a memory device to implement protocol(s), protocol layers,communication drivers, device drivers, combinations thereof, and/or thelike. A firmware interface may include a combination of embeddedhardware and code stored in and/or in communication with a memory deviceto implement connections, electronic device operations, protocol(s),protocol layers, communication drivers, device drivers, hardwareoperations, combinations thereof, and/or the like.

The term configured may relate to the capacity of a device whether thedevice is in an operational or a non-operational state. Configured mayalso refer to specific settings in a device that effect the operationalcharacteristics of the device whether the device is in an operational ora non-operational state. In other words, the hardware, software,firmware, registers, memory values, and/or the like may be “configured”within a device, whether the device is in an operational or anonoperational state, to provide the device with specificcharacteristics. Terms such as “a control message to cause in a device”may mean that a control message has parameters that may be used toconfigure specific characteristics in the device, whether the device isin an operational or a non-operational state.

A 5G network may include a multitude of base stations, providing a userplane NR PDCP/NR RLC/NR MAC/NR PHY and control plane (NR RRC) protocolterminations towards the wireless device. The base station(s) may beinterconnected with other base station(s) (e.g., employing an Xninterface). The base stations may also be connected employing, forexample, an NG interface to an NGC. FIG. 10A and FIG. 10B show examplesfor interfaces between a 5G core network (e.g., NGC) and base stations(e.g., gNB and eLTE eNB). For example, the base stations may beinterconnected to the NGC control plane (e.g., NG CP) employing the NG-Cinterface and to the NGC user plane (e.g., UPGW) employing the NG-Uinterface. The NG interface may support a many-to-many relation between5G core networks and base stations.

A base station may include many sectors, for example: 1, 2, 3, 4, or 6sectors. A base station may include many cells, for example, rangingfrom 1 to 50 cells or more. A cell may be categorized, for example, as aprimary cell or secondary cell. At RRC connectionestablishment/re-establishment/handover, one serving cell may providethe NAS (non-access stratum) mobility information (e.g., TAI), and atRRC connection re-establishment/handover, one serving cell may providethe security input. This cell may be referred to as the Primary Cell(PCell). In the downlink, the carrier corresponding to the PCell may bethe Downlink Primary Component Carrier (DL PCC), while in the uplink, itmay be the Uplink Primary Component Carrier (UL PCC). Depending onwireless device capabilities, Secondary Cells (SCells) may be configuredto form together with the PCell a set of serving cells. In the downlink,the carrier corresponding to an SCell may be a Downlink SecondaryComponent Carrier (DL SCC), while in the uplink, it may be an UplinkSecondary Component Carrier (UL SCC). An SCell may or may not have anuplink carrier.

A cell, comprising a downlink carrier and optionally an uplink carrier,may be assigned a physical cell ID and a cell index. A carrier (downlinkor uplink) may belong to only one cell. The cell ID or cell index mayalso identify the downlink carrier or uplink carrier of the cell(depending on the context it is used). The cell ID may be equallyreferred to a carrier ID, and cell index may be referred to carrierindex. In implementation, the physical cell ID or cell index may beassigned to a cell. A cell ID may be determined using a synchronizationsignal transmitted on a downlink carrier. A cell index may be determinedusing RRC messages. For example, reference to a first physical cell IDfor a first downlink carrier may indicate that the first physical cellID is for a cell comprising the first downlink carrier. The same conceptmay apply to, for example, carrier activation. Reference to a firstcarrier that is activated may indicate that the cell comprising thefirst carrier is activated.

Examples may be configured to operate as needed. The disclosedmechanisms may be performed when certain criteria are met, for example,in a wireless device, a base station, a radio environment, a network, acombination of the above, and/or the like. Example criteria may bebased, at least in part, on for example, traffic load, initial systemset up, packet sizes, traffic characteristics, a combination of theabove, and/or the like. When the one or more criteria are met, variousexamples may be applied. Therefore, it may be possible to implementexamples that selectively implement disclosed protocols.

A base station may communicate with a mix of wireless devices. Wirelessdevices may support multiple technologies, and/or multiple releases ofthe same technology. Wireless devices may have some specificcapability(ies) depending on its wireless device category and/orcapability(ies). A base station may comprise multiple sectors. Referenceto a base station communicating with a plurality of wireless devices mayindicate that a subset of the total wireless devices in a coverage area.A plurality of wireless devices of a given LTE or 5G release, with agiven capability and in a given sector of the base station, may be used.The plurality of wireless devices may refer to a selected plurality ofwireless devices, and/or a subset of total wireless devices in acoverage area which perform according to disclosed methods, and/or thelike. There may be a plurality of wireless devices in a coverage areathat may not comply with the disclosed methods, for example, becausethose wireless devices perform based on older releases of LTE or 5Gtechnology.

A base station may transmit (e.g., to a wireless device) one or moremessages (e.g. RRC messages) that may comprise a plurality ofconfiguration parameters for one or more cells. One or more cells maycomprise at least one primary cell and at least one secondary cell. Inan example, an RRC message may be broadcasted or unicasted to thewireless device. In an example, configuration parameters may comprisecommon parameters and dedicated parameters.

Services and/or functions of an RRC sublayer may comprise at least oneof: broadcast of system information related to AS and NAS; paginginitiated by 5GC and/or NG-RAN; establishment, maintenance, and/orrelease of an RRC connection between a wireless device and NG-RAN, whichmay comprise at least one of addition, modification and release ofcarrier aggregation; or addition, modification, and/or release of dualconnectivity in NR or between E-UTRA and NR. Services and/or functionsof an RRC sublayer may further comprise at least one of securityfunctions comprising key management; establishment, configuration,maintenance, and/or release of Signaling Radio Bearers (SRBs) and/orData Radio Bearers (DRBs); mobility functions which may comprise atleast one of a handover (e.g. intra NR mobility or inter-RAT mobility)and a context transfer; or a wireless device cell selection andreselection and control of cell selection and reselection. Servicesand/or functions of an RRC sublayer may further comprise at least one ofQoS management functions; a wireless device measurementconfiguration/reporting; detection of and/or recovery from radio linkfailure; or NAS message transfer to/from a core network entity (e.g.AMF, Mobility Management Entity (MME)) from/to the wireless device.

An RRC sublayer may support an RRC_Idle state, an RRC_Inactive stateand/or an RRC_Connected state for a wireless device. In an RRC_Idlestate, a wireless device may perform at least one of: Public Land MobileNetwork (PLMN) selection; receiving broadcasted system information; cellselection/re-selection; monitoring/receiving a paging for mobileterminated data initiated by 5GC; paging for mobile terminated data areamanaged by 5GC; or DRX for CN paging configured via NAS. In anRRC_Inactive state, a wireless device may perform at least one of:receiving broadcasted system information; cell selection/re-selection;monitoring/receiving a RAN/CN paging initiated by NG-RAN/5GC; RAN-basednotification area (RNA) managed by NG-RAN; or DRX for RAN/CN pagingconfigured by NG-RAN/NAS. In an RRC_Idle state of a wireless device, abase station (e.g. NG-RAN) may keep a 5GC-NG-RAN connection (bothC/U-planes) for the wireless device; and/or store a UE AS context forthe wireless device. In an RRC_Connected state of a wireless device, abase station (e.g. NG-RAN) may perform at least one of: establishment of5GC-NG-RAN connection (both C/U-planes) for the wireless device; storinga UE AS context for the wireless device; transmit/receive of unicastdata to/from the wireless device; or network-controlled mobility basedon measurement results received from the wireless device. In anRRC_Connected state of a wireless device, an NG-RAN may know a cell thatthe wireless device belongs to.

System information (SI) may be divided into minimum SI and other SI. Theminimum SI may be periodically broadcast. The minimum SI may comprisebasic information required for initial access and information foracquiring any other SI broadcast periodically or provisioned on-demand,i.e. scheduling information. The other SI may either be broadcast, or beprovisioned in a dedicated manner, either triggered by a network or uponrequest from a wireless device. A minimum SI may be transmitted via twodifferent downlink channels using different messages (e.g.MasterInformationBlock and SystemInformationBlockType1). The other SImay be transmitted via SystemInformationBlockType2. For a wirelessdevice in an RRC_Connected state, dedicated RRC signaling may beemployed for the request and delivery of the other SI. For the wirelessdevice in the RRC_Idle state and/or the RRC_Inactive state, the requestmay trigger a random-access procedure.

A wireless device may report its radio access capability informationwhich may be static. A base station may request what capabilities for awireless device to report based on band information. When allowed by anetwork, a temporary capability restriction request may be sent by thewireless device to signal the limited availability of some capabilities(e.g. due to hardware sharing, interference or overheating) to the basestation. The base station may confirm or reject the request. Thetemporary capability restriction may be transparent to 5GC (e.g., staticcapabilities may be stored in 5GC).

When CA is configured, a wireless device may have an RRC connection witha network. At RRC connection establishment/re-establishment/handoverprocedure, one serving cell may provide NAS mobility information, and atRRC connection re-establishment/handover, one serving cell may provide asecurity input. This cell may be referred to as the PCell. Depending onthe capabilities of the wireless device, SCells may be configured toform together with the PCell a set of serving cells. The configured setof serving cells for the wireless device may comprise one PCell and oneor more SCells.

The reconfiguration, addition and removal of SCells may be performed byRRC. At intra-NR handover, RRC may also add, remove, or reconfigureSCells for usage with the target PCell. When adding a new SCell,dedicated RRC signaling may be employed to send all required systeminformation of the SCell. While in connected mode, wireless devices maynot need to acquire broadcasted system information directly from theSCells.

The purpose of an RRC connection reconfiguration procedure may be tomodify an RRC connection, (e.g. to establish, modify and/or release RBs,to perform handover, to setup, modify, and/or release measurements, toadd, modify, and/or release SCells and cell groups). As part of the RRCconnection reconfiguration procedure, NAS dedicated information may betransferred from the network to the wireless device. TheRRCConnectionReconfiguration message may be a command to modify an RRCconnection. It may convey information for measurement configuration,mobility control, radio resource configuration (e.g. RBs, MAC mainconfiguration and physical channel configuration) comprising anyassociated dedicated NAS information and security configuration. If thereceived RRC Connection Reconfiguration message includes thesCellToReleaseList, the wireless device may perform an SCell release. Ifthe received RRC Connection Reconfiguration message includes thesCellToAddModList, the wireless device may perform SCell additions ormodification.

An RRC connection establishment (or reestablishment, resume) proceduremay be to establish (or reestablish, resume) an RRC connection. an RRCconnection establishment procedure may comprise SRB1 establishment. TheRRC connection establishment procedure may be used to transfer theinitial NAS dedicated information message from a wireless device toE-UTRAN. The RRCConnectionReestablishment message may be used tore-establish SRB1.

A measurement report procedure may be to transfer measurement resultsfrom a wireless device to NG-RAN. The wireless device may initiate ameasurement report procedure after successful security activation. Ameasurement report message may be employed to transmit measurementresults.

FIG. 5A, FIG. 5B, FIG. 5C, and FIG. 5D show examples for uplink anddownlink signal transmission. FIG. 5A shows an example for an uplinkphysical channel. The baseband signal representing the physical uplinkshared channel may be processed according to the following processes,which may be performed by structures described below. While thesestructures and corresponding functions are shown as examples, it isanticipated that other structures and/or functions may be implemented invarious examples. The structures and corresponding functions maycomprise, e.g., one or more scrambling devices 501A and 501B configuredto perform scrambling of coded bits in each of the codewords to betransmitted on a physical channel; one or more modulation mappers 502Aand 502B configured to perform modulation of scrambled bits to generatecomplex-valued symbols; a layer mapper 503 configured to perform mappingof the complex-valued modulation symbols onto one or severaltransmission layers; one or more transform precoders 504A and 504B togenerate complex-valued symbols; a precoding device 505 configured toperform precoding of the complex-valued symbols; one or more resourceelement mappers 506A and 506B configured to perform mapping of precodedcomplex-valued symbols to resource elements; one or more signalgenerators 507A and 507B configured to perform the generation of acomplex-valued time-domain DFTS-OFDM/SC-FDMA signal for each antennaport; and/or the like.

Example modulation and up-conversion to the carrier frequency of thecomplex-valued DFTS-OFDM/SC-FDMA baseband signal for each antenna portand/or the complex-valued physical random access channel (PRACH)baseband signal is shown in FIG. 5B. For example, the baseband signal,represented as s₁(t), may be split, by a signal splitter 510, into realand imaginary components, Re {s₁(t)} and Im {s₁(t)}, respectively. Thereal component may be modulated by a modulator 511A, and the imaginarycomponent may be modulated by a modulator 511B. The output signal of themodulator 511A and the output signal of the modulator 511B may be mixedby a mixer 512. The output signal of the mixer 512 may be input to afiltering device 513, and filtering may be employed by the filteringdevice 513 prior to transmission.

An example structure for downlink transmissions is shown in FIG. 5C. Thebaseband signal representing a downlink physical channel may beprocessed by the following processes, which may be performed bystructures described below. While these structures and correspondingfunctions are shown as examples, it is anticipated that other structuresand/or functions may be implemented in various examples. The structuresand corresponding functions may comprise, e.g., one or more scramblingdevices 531A and 531B configured to perform scrambling of coded bits ineach of the codewords to be transmitted on a physical channel; one ormore modulation mappers 532A and 532B configured to perform modulationof scrambled bits to generate complex-valued modulation symbols; a layermapper 533 configured to perform mapping of the complex-valuedmodulation symbols onto one or several transmission layers; a precodingdevice 534 configured to perform precoding of the complex-valuedmodulation symbols on each layer for transmission on the antenna ports;one or more resource element mappers 535A and 535B configured to performmapping of complex-valued modulation symbols for each antenna port toresource elements; one or more OFDM signal generators 536A and 536Bconfigured to perform the generation of complex-valued time-domain OFDMsignal for each antenna port; and/or the like.

Example modulation and up-conversion to the carrier frequency of thecomplex-valued OFDM baseband signal for each antenna port is shown inFIG. 5D. For example, the baseband signal, represented as s₁ ^((p))(t),may be split, by a signal splitter 520, into real and imaginarycomponents, Re{s₁ ^((p))(t)} and Im{s₁ ^((p))(t)}, respectively. Thereal component may be modulated by a modulator 521A, and the imaginarycomponent may be modulated by a modulator 521B. The output signal of themodulator 521A and the output signal of the modulator 521B may be mixedby a mixer 522. The output signal of the mixer 522 may be input to afiltering device 523, and filtering may be employed by the filteringdevice 523 prior to transmission.

FIG. 6 and FIG. 7 show examples for protocol structures with CA andmulti-connectivity. In FIG. 6, NR may support multi-connectivityoperation, whereby a multiple receiver/transmitter (RX/TX) UE inRRC_CONNECTED may be configured to utilize radio resources provided bymultiple schedulers located in multiple gNBs connected via a non-idealor ideal backhaul over the Xn interface. gNBs involved inmulti-connectivity for a certain UE may assume two different roles: agNB may either act as a master gNB (e.g., 600) or as a secondary gNB(e.g., 610 or 620). In multi-connectivity, a UE may be connected to onemaster gNB (e.g., 600) and one or more secondary gNBs (e.g., 610 and/or620). Any one or more of the Master gNB 600 and/or the secondary gNBs610 and 620 may be a Next Generation (NG) NodeB. The master gNB 600 maycomprise protocol layers NR MAC 601, NR RLC 602 and 603, and NR PDCP 604and 605. The secondary gNB may comprise protocol layers NR MAC 611, NRRLC 612 and 613, and NR PDCP 614. The secondary gNB may compriseprotocol layers NR MAC 621, NR RLC 622 and 623, and NR PDCP 624. Themaster gNB 600 may communicate via an interface 606 and/or via aninterface 607, the secondary gNB 610 may communicate via an interface615, and the secondary gNB 620 may communicate via an interface 625. Themaster gNB 600 may also communicate with the secondary gNB 610 and thesecondary gNB 621 via interfaces 608 and 609, respectively, which mayinclude Xn interfaces. For example, the master gNB 600 may communicatevia the interface 608, at layer NR PDCP 605, with the secondary gNB 610at layer NR RLC 612. The master gNB 600 may communicate via theinterface 609, at layer NR PDCP 605, with the secondary gNB 620 at layerNR RLC 622.

FIG. 7 shows an example structure for the UE side MAC entities, e.g., ifa Master Cell Group (MCG) and a Secondary Cell Group (SCG) areconfigured. Media Broadcast Multicast Service (MBMS) reception may beincluded but is not shown in this figure for simplicity.

In multi-connectivity, the radio protocol architecture that a particularbearer uses may depend on how the bearer is set up. As an example, threealternatives may exist, an MCG bearer, an SCG bearer, and a splitbearer, such as shown in FIG. 6. NR RRC may be located in a master gNBand SRBs may be configured as a MCG bearer type and may use the radioresources of the master gNB. Multi-connectivity may have at least onebearer configured to use radio resources provided by the secondary gNB.Multi-connectivity may or may not be configured or implemented.

In the case of multi-connectivity, the UE may be configured withmultiple NR MAC entities: e.g., one NR MAC entity for a master gNB, andother NR MAC entities for secondary gNBs. In multi-connectivity, theconfigured set of serving cells for a UE may comprise two subsets: e.g.,the Master Cell Group (MCG) containing the serving cells of the mastergNB, and the Secondary Cell Groups (SCGs) containing the serving cellsof the secondary gNBs.

For an SCG, one or more of the following may be applied. At least onecell in the SCG may have a configured UL component carrier (CC) and oneof the UL CCs, e g, named PSCell (or PCell of SCG, or sometimes calledPCell), may be configured with PUCCH resources. If the SCG isconfigured, there may be at least one SCG bearer or one split bearer. Ifa physical layer problem or a random access problem on a PSCell occursor is detected, if the maximum number of NR RLC retransmissions has beenreached associated with the SCG, or if an access problem on a PSCellduring a SCG addition or a SCG change occurs or is detected, then an RRCconnection re-establishment procedure may not be triggered, ULtransmissions towards cells of the SCG may be stopped, a master gNB maybe informed by the UE of a SCG failure type, and for a split bearer theDL data transfer over the master gNB may be maintained. The NR RLCAcknowledge Mode (AM) bearer may be configured for the split bearer.Like the PCell, a PSCell may not be de-activated. The PSCell may bechanged with an SCG change (e.g., with a security key change and a RACHprocedure). A direct bearer type may change between a split bearer andan SCG bearer, or a simultaneous configuration of an SCG and a splitbearer may or may not be supported.

With respect to the interaction between a master gNB and secondary gNBsfor multi-connectivity, one or more of the following principles may beapplied. The master gNB may maintain the RRM measurement configurationof the UE, and the master gNB may, (e.g., based on received measurementreports, and/or based on traffic conditions and/or bearer types), decideto ask a secondary gNB to provide additional resources (e.g., servingcells) for a UE. If a request from the master gNB is received, asecondary gNB may create a container that may result in theconfiguration of additional serving cells for the UE (or the secondarygNB decide that it has no resource available to do so). For UEcapability coordination, the master gNB may provide some or all of theActive Set (AS) configuration and the UE capabilities to the secondarygNB. The master gNB and the secondary gNB may exchange information abouta UE configuration, such as by employing NR RRC containers (e.g.,inter-node messages) carried in Xn messages. The secondary gNB mayinitiate a reconfiguration of its existing serving cells (e.g., PUCCHtowards the secondary gNB). The secondary gNB may decide which cell isthe PSCell within the SCG. The master gNB may or may not change thecontent of the NR RRC configuration provided by the secondary gNB. Inthe case of an SCG addition and an SCG SCell addition, the master gNBmay provide the latest measurement results for the SCG cell(s). Both amaster gNB and a secondary gNBs may know the system frame number (SFN)and subframe offset of each other by operations, administration, andmaintenance (OAM) (e.g., for the purpose of discontinuous reception(DRX) alignment and identification of a measurement gap). In an example,when adding a new SCG SCell, dedicated NR RRC signaling may be used forsending required system information of the cell for CA, except, e.g.,for the SFN acquired from an MIB of the PSCell of an SCG.

FIG. 7 shows an example of dual-connectivity (DC) for two MAC entitiesat a UE side. A first MAC entity may comprise a lower layer of an MCG700, an upper layer of an MCG 718, and one or more intermediate layersof an MCG 719. The lower layer of the MCG 700 may comprise, e.g., apaging channel (PCH) 701, a broadcast channel (BCH) 702, a downlinkshared channel (DL-SCH) 703, an uplink shared channel (UL-SCH) 704, anda random access channel (RACH) 705. The one or more intermediate layersof the MCG 719 may comprise, e.g., one or more hybrid automatic repeatrequest (HARQ) processes 706, one or more random access controlprocesses 707, multiplexing and/or de-multiplexing processes 709,logical channel prioritization on the uplink processes 710, and acontrol processes 708 providing control for the above processes in theone or more intermediate layers of the MCG 719. The upper layer of theMCG 718 may comprise, e.g., a paging control channel (PCCH) 711, abroadcast control channel (BCCH) 712, a common control channel (CCCH)713, a dedicated control channel (DCCH) 714, a dedicated traffic channel(DTCH) 715, and a MAC control 716.

A second MAC entity may comprise a lower layer of an SCG 720, an upperlayer of an SCG 738, and one or more intermediate layers of an SCG 739.The lower layer of the SCG 720 may comprise, e.g., a BCH 722, a DL-SCH723, an UL-SCH 724, and a RACH 725. The one or more intermediate layersof the SCG 739 may comprise, e.g., one or more HARQ processes 726, oneor more random access control processes 727, multiplexing and/orde-multiplexing processes 729, logical channel prioritization on theuplink processes 730, and a control processes 728 providing control forthe above processes in the one or more intermediate layers of the SCG739. The upper layer of the SCG 738 may comprise, e.g., a BCCH 732, aDCCH 714, a DTCH 735, and a MAC control 736.

Serving cells may be grouped in a TA group (TAG). Serving cells in oneTAG may use the same timing reference. For a given TAG, user equipment(UE) may use at least one downlink carrier as a timing reference. For agiven TAG, a UE may synchronize uplink subframe and frame transmissiontiming of uplink carriers belonging to the same TAG. In an example,serving cells having an uplink to which the same TA applies maycorrespond to serving cells hosted by the same receiver. A UE supportingmultiple TAs may support two or more TA groups. One TA group may containthe PCell and may be called a primary TAG (pTAG). In a multiple TAGconfiguration, at least one TA group may not contain the PCell and maybe called a secondary TAG (sTAG). In an example, carriers within thesame TA group may use the same TA value and/or the same timingreference. When DC is configured, cells belonging to a cell group (e.g.,MCG or SCG) may be grouped into multiple TAGs including a pTAG and oneor more sTAGs.

FIG. 8 shows example TAG configurations. In Example 1, a pTAG comprisesa PCell, and an sTAG comprises an SCell1. In Example 2, a pTAG comprisesa PCell and an SCell1, and an sTAG comprises an SCell2 and an SCell3. InExample 3, a pTAG comprises a PCell and an SCell1, and an sTAG1comprises an SCell2 and an SCell3, and an sTAG2 comprises a SCell4. Upto four TAGs may be supported in a cell group (MCG or SCG), and otherexample TAG configurations may also be provided. In various examples,structures and operations are described for use with a pTAG and an sTAG.Some of the examples may be applied to configurations with multiplesTAGs.

In an example, an eNB may initiate an RA procedure, via a PDCCH order,for an activated SCell. The PDCCH order may be sent on a scheduling cellof this SCell. When cross carrier scheduling is configured for a cell,the scheduling cell may be different than the cell that is employed forpreamble transmission, and the PDCCH order may include an SCell index.At least a non-contention based RA procedure may be supported forSCell(s) assigned to sTAG(s).

FIG. 9 shows an example of random access processes, and a correspondingmessage flow, in a secondary TAG. A base station, such as an eNB, maytransmit an activation command 900 to a wireless device, such as a UE.The activation command 900 may be transmitted to activate an SCell. Thebase station may also transmit a PDDCH order 901 to the wireless device,which may be transmitted after the activation command 900. The wirelessdevice may begin to perform a RACH process for the SCell, which may beinitiated after receiving the PDDCH order 901. The RACH process mayinclude the wireless device transmitting to the base station a preamble902 (e.g., Msg1), such as a random access preamble (RAP). The preamble902 may be transmitted in response to the PDCCH order 901. The wirelessdevice may transmit the preamble 902 via an SCell belonging to an sTAG.In an example, preamble transmission for SCells may be controlled by anetwork using PDCCH format 1A. The base station may send a random accessresponse (RAR) 903 (e.g., Msg2 message) to the wireless device. The RAR903 may be in response to the preamble 902 transmission via the SCell.The RAR 903 may be addressed to a random access radio network temporaryidentifier (RA-RNTI) in a PCell common search space (CSS). If thewireless device receives the RAR 903, the RACH process may conclude. TheRACH process may conclude after or in response to the wireless devicereceiving the RAR 903 from the base station. After the RACH process, thewireless device may transmit an uplink transmission 904. The uplinktransmission 904 may comprise uplink packets transmitted via the sameSCell used for the preamble 902 transmission.

Initial timing alignment for communications between the wireless deviceand the base station may be achieved through a random access procedure,such as described above regarding FIG. 9. The random access proceduremay involve a wireless device, such as a UE, transmitting a randomaccess preamble and a base station, such as an eNB, responding with aninitial TA command NTA (amount of timing advance) within a random accessresponse window. The start of the random access preamble may be alignedwith the start of a corresponding uplink subframe at the UE assumingNTA=0. The eNB may estimate the uplink timing from the random accesspreamble transmitted by the UE. The TA command may be derived by the eNBbased on the estimation of the difference between the desired UL timingand the actual UL timing. The UE may determine the initial uplinktransmission timing relative to the corresponding downlink of the sTAGon which the preamble is transmitted.

The mapping of a serving cell to a TAG may be configured by a servingeNB with RRC signaling. The mechanism for TAG configuration andreconfiguration may be based on RRC signaling. If an eNB performs anSCell addition configuration, the related TAG configuration may beconfigured for the SCell. An eNB may modify the TAG configuration of anSCell by removing (e.g., releasing) the SCell and adding (e.g.,configuring) a new SCell (with the same physical cell ID and frequency)with an updated TAG ID. The new SCell with the updated TAG ID mayinitially be inactive subsequent to being assigned the updated TAG ID.The eNB may activate the updated new SCell and start scheduling packetson the activated SCell. In some examples, it may not be possible tochange the TAG associated with an SCell, but rather, the SCell may needto be removed and a new SCell may need to be added with another TAG. Forexample, if there is a need to move an SCell from an sTAG to a pTAG, atleast one RRC message, such as at least one RRC reconfiguration message,may be sent to the UE. The at least one RRC message may be sent to theUE to reconfigure TAG configurations, e.g., by releasing the SCell andthen configuring the SCell as a part of the pTAG. If, e.g., an SCell isadded or configured without a TAG index, the SCell may be explicitlyassigned to the pTAG. The PCell may not change its TA group and may be amember of the pTAG.

In LTE Release-10 and Release-11 CA, a PUCCH transmission is onlytransmitted on a PCell (e.g., a PSCell) to an eNB. In LTE-Release 12 andearlier, a UE may transmit PUCCH information on one cell (e.g., a PCellor a PSCell) to a given eNB. As the number of CA capable UEs increase,and as the number of aggregated carriers increase, the number of PUCCHsand the PUCCH payload size may increase. Accommodating the PUCCHtransmissions on the PCell may lead to a high PUCCH load on the PCell. APUCCH on an SCell may be introduced to offload the PUCCH resource fromthe PCell. More than one PUCCH may be configured. For example, a PUCCHon a PCell may be configured and another PUCCH on an SCell may beconfigured. One, two, or more cells may be configured with PUCCHresources for transmitting CSI, acknowledgment (ACK), and/ornon-acknowledgment (NACK) to a base station. Cells may be grouped intomultiple PUCCH groups, and one or more cell within a group may beconfigured with a PUCCH. In some examples, one SCell may belong to onePUCCH group. SCells with a configured PUCCH transmitted to a basestation may be called a PUCCH SCell, and a cell group with a commonPUCCH resource transmitted to the same base station may be called aPUCCH group.

A MAC entity may have a configurable timer, e.g., timeAlignmentTimer,per TAG. The timeAlignmentTimer may be used to control how long the MACentity considers the serving cells belonging to the associated TAG to beuplink time aligned. If a Timing Advance Command MAC control element isreceived, the MAC entity may apply the Timing Advance Command for theindicated TAG; and/or the MAC entity may start or restart thetimeAlignmentTimer associated with a TAG that may be indicated by theTiming Advance Command MAC control element. If a Timing Advance Commandis received in a Random Access Response message for a serving cellbelonging to a TAG, the MAC entity may apply the Timing Advance Commandfor this TAG and/or start or restart the timeAlignmentTimer associatedwith this TAG. Additionally or alternatively, if the Random AccessPreamble is not selected by the MAC entity, the MAC entity may apply theTiming Advance Command for this TAG and/or start or restart thetimeAlignmentTimer associated with this TAG. If the timeAlignmentTimerassociated with this TAG is not running, the Timing Advance Command forthis TAG may be applied, and the timeAlignmentTimer associated with thisTAG may be started. If the contention resolution is not successful, atimeAlignmentTimer associated with this TAG may be stopped. If thecontention resolution is successful, the MAC entity may ignore thereceived Timing Advance Command. The MAC entity may determine whetherthe contention resolution is successful or whether the contentionresolution is not successful.

FIG. 10A and FIG. 10B show examples for interfaces between a 5G corenetwork (e.g., NGC) and base stations (e.g., gNB and eLTE eNB). Forexample, in FIG. 10A, a base station, such as a gNB 1020, may beinterconnected to an NGC 1010 control plane employing an NG-C interface.The base station, e.g., the gNB 1020, may also be interconnected to anNGC 1010 user plane (e.g., UPGW) employing an NG-U interface. As anotherexample, in FIG. 10B, a base station, such as an eLTE eNB 1040, may beinterconnected to an NGC 1030 control plane employing an NG-C interface.The base station, e.g., the eLTE eNB 1040, may also be interconnected toan NGC 1030 user plane (e.g., UPGW) employing an NG-U interface. An NGinterface may support a many-to-many relation between 5G core networksand base stations.

FIG. 11A, FIG. 11B, FIG. 11C, FIG. 11D, FIG. 11E, and FIG. 11F areexamples for architectures of tight interworking between a 5G RAN and anLTE RAN. The tight interworking may enable a multiplereceiver/transmitter (RX/TX) UE in an RRC_CONNECTED state to beconfigured to utilize radio resources provided by two schedulers locatedin two base stations (e.g., an eLTE eNB and a gNB). The two basestations may be connected via a non-ideal or ideal backhaul over the Xxinterface between an LTE eNB and a gNB, or over the Xn interface betweenan eLTE eNB and a gNB. Base stations involved in tight interworking fora certain UE may assume different roles. For example, a base station mayact as a master base station or a base station may act as a secondarybase station. In tight interworking, a UE may be connected to both amaster base station and a secondary base station. Mechanisms implementedin tight interworking may be extended to cover more than two basestations.

In FIG. 11A and FIG. 11B, a master base station may be an LTE eNB 1102Aor an LTE eNB 1102B, which may be connected to EPC nodes 1101A or 1101B,respectively. This connection to EPC nodes may be, e.g., to an MME viathe S1-C interface and/or to an S-GW via the S1-U interface. A secondarybase station may be a gNB 1103A or a gNB 1103B, either or both of whichmay be a non-standalone node having a control plane connection via anXx-C interface to an LTE eNB (e.g., the LTE eNB 1102A or the LTE eNB1102B). In the tight interworking architecture of FIG. 11A, a user planefor a gNB (e.g., the gNB 1103A) may be connected to an S-GW (e.g., theEPC 1101A) through an LTE eNB (e.g., the LTE eNB 1102A), via an Xx-Uinterface between the LTE eNB and the gNB, and via an S1-U interfacebetween the LTE eNB and the S-GW. In the architecture of FIG. 11B, auser plane for a gNB (e.g., the gNB 1103B) may be connected directly toan S-GW (e.g., the EPC 1101B) via an S1-U interface between the gNB andthe S-GW.

In FIG. 11C and FIG. 11D, a master base station may be a gNB 1103C or agNB 1103D, which may be connected to NGC nodes 1101C or 1101D,respectively. This connection to NGC nodes may be, e.g., to a controlplane core node via the NG-C interface and/or to a user plane core nodevia the NG-U interface. A secondary base station may be an eLTE eNB1102C or an eLTE eNB 1102D, either or both of which may be anon-standalone node having a control plane connection via an Xn-Cinterface to a gNB (e.g., the gNB 1103C or the gNB 1103D). In the tightinterworking architecture of FIG. 11C, a user plane for an eLTE eNB(e.g., the eLTE eNB 1102C) may be connected to a user plane core node(e.g., the NGC 1101C) through a gNB (e.g., the gNB 1103C), via an Xn-Uinterface between the eLTE eNB and the gNB, and via an NG-U interfacebetween the gNB and the user plane core node. In the architecture ofFIG. 11D, a user plane for an eLTE eNB (e.g., the eLTE eNB 1102D) may beconnected directly to a user plane core node (e.g., the NGC 1101D) viaan NG-U interface between the eLTE eNB and the user plane core node.

In FIG. 11E and FIG. 11F, a master base station may be an eLTE eNB 1102Eor an eLTE eNB 1102F, which may be connected to NGC nodes 1101E or1101F, respectively. This connection to NGC nodes may be, e.g., to acontrol plane core node via the NG-C interface and/or to a user planecore node via the NG-U interface. A secondary base station may be a gNB1103E or a gNB 1103F, either or both of which may be a non-standalonenode having a control plane connection via an Xn-C interface to an eLTEeNB (e.g., the eLTE eNB 1102E or the eLTE eNB 1102F). In the tightinterworking architecture of FIG. 11E, a user plane for a gNB (e.g., thegNB 1103E) may be connected to a user plane core node (e.g., the NGC1101E) through an eLTE eNB (e.g., the eLTE eNB 1102E), via an Xn-Uinterface between the eLTE eNB and the gNB, and via an NG-U interfacebetween the eLTE eNB and the user plane core node. In the architectureof FIG. 11F, a user plane for a gNB (e.g., the gNB 1103F) may beconnected directly to a user plane core node (e.g., the NGC 1101F) viaan NG-U interface between the gNB and the user plane core node.

FIG. 12A, FIG. 12B, and FIG. 12C are examples for radio protocolstructures of tight interworking bearers.

In FIG. 12A, an LTE eNB 1201A may be an S1 master base station, and agNB 1210A may be an S1 secondary base station. An example for a radioprotocol architecture for a split bearer and an SCG bearer is shown. TheLTE eNB 1201A may be connected to an EPC with a non-standalone gNB1210A, via an Xx interface between the PDCP 1206A and an NR RLC 1212A.The LTE eNB 1201A may include protocol layers MAC 1202A, RLC 1203A andRLC 1204A, and PDCP 1205A and PDCP 1206A. An MCG bearer type mayinterface with the PDCP 1205A, and a split bearer type may interfacewith the PDCP 1206A. The gNB 1210A may include protocol layers NR MAC1211A, NR RLC 1212A and NR RLC 1213A, and NR PDCP 1214A. An SCG bearertype may interface with the NR PDCP 1214A.

In FIG. 12B, a gNB 1201B may be an NG master base station, and an eLTEeNB 1210B may be an NG secondary base station. An example for a radioprotocol architecture for a split bearer and an SCG bearer is shown. ThegNB 1201B may be connected to an NGC with a non-standalone eLTE eNB1210B, via an Xn interface between the NR PDCP 1206B and an RLC 1212B.The gNB 1201B may include protocol layers NR MAC 1202B, NR RLC 1203B andNR RLC 1204B, and NR PDCP 1205B and NR PDCP 1206B. An MCG bearer typemay interface with the NR PDCP 1205B, and a split bearer type mayinterface with the NR PDCP 1206B. The eLTE eNB 1210B may includeprotocol layers MAC 1211B, RLC 1212B and RLC 1213B, and PDCP 1214B. AnSCG bearer type may interface with the PDCP 1214B.

In FIG. 12C, an eLTE eNB 1201C may be an NG master base station, and agNB 1210C may be an NG secondary base station. An example for a radioprotocol architecture for a split bearer and an SCG bearer is shown. TheeLTE eNB 1201C may be connected to an NGC with a non-standalone gNB1210C, via an Xn interface between the PDCP 1206C and an NR RLC 1212C.The eLTE eNB 1201C may include protocol layers MAC 1202C, RLC 1203C andRLC 1204C, and PDCP 1205C and PDCP 1206C. An MCG bearer type mayinterface with the PDCP 1205C, and a split bearer type may interfacewith the PDCP 1206C. The gNB 1210C may include protocol layers NR MAC1211C, NR RLC 1212C and NR RLC 1213C, and NR PDCP 1214C. An SCG bearertype may interface with the NR PDCP 1214C.

In a 5G network, the radio protocol architecture that a particularbearer uses may depend on how the bearer is setup. At least threealternatives may exist, e.g., an MCG bearer, an SCG bearer, and a splitbearer, such as shown in FIG. 12A, FIG. 12B, and FIG. 12C. The NR RRCmay be located in a master base station, and the SRBs may be configuredas an MCG bearer type and may use the radio resources of the master basestation. Tight interworking may have at least one bearer configured touse radio resources provided by the secondary base station. Tightinterworking may or may not be configured or implemented.

In the case of tight interworking, the UE may be configured with two MACentities: e.g., one MAC entity for a master base station, and one MACentity for a secondary base station. In tight interworking, theconfigured set of serving cells for a UE may comprise of two subsets:e.g., the Master Cell Group (MCG) containing the serving cells of themaster base station, and the Secondary Cell Group (SCG) containing theserving cells of the secondary base station.

For an SCG, one or more of the following may be applied. At least onecell in the SCG may have a configured UL CC and one of them, e.g., aPSCell (or the PCell of the SCG, which may also be called a PCell), isconfigured with PUCCH resources. If the SCG is configured, there may beat least one SCG bearer or one split bearer. If one or more of aphysical layer problem or a random access problem is detected on aPSCell, if the maximum number of (NR) RLC retransmissions associatedwith the SCG has been reached, and/or if an access problem on a PSCellduring an SCG addition or during an SCG change is detected, then: an RRCconnection re-establishment procedure may not be triggered, ULtransmissions towards cells of the SCG may be stopped, a master basestation may be informed by the UE of a SCG failure type, and/or for asplit bearer the DL data transfer over the master base station may bemaintained. The RLC AM bearer may be configured for the split bearer.Like the PCell, a PSCell may not be de-activated. A PSCell may bechanged with an SCG change, e.g., with security key change and a RACHprocedure. A direct bearer type change, between a split bearer and anSCG bearer, may not be supported. Simultaneous configuration of an SCGand a split bearer may not be supported.

With respect to the interaction between a master base station and asecondary base station, one or more of the following principles may beapplied. The master base station may maintain the RRM measurementconfiguration of the UE. The master base station may determine to ask asecondary base station to provide additional resources (e.g., servingcells) for a UE. This determination may be based on, e.g., receivedmeasurement reports, traffic conditions, and/or bearer types. If arequest from the master base station is received, a secondary basestation may create a container that may result in the configuration ofadditional serving cells for the UE, or the secondary base station maydetermine that it has no resource available to do so. The master basestation may provide at least part of the AS configuration and the UEcapabilities to the secondary base station, e.g., for UE capabilitycoordination. The master base station and the secondary base station mayexchange information about a UE configuration such as by using RRCcontainers (e.g., inter-node messages) carried in Xn or Xx messages. Thesecondary base station may initiate a reconfiguration of its existingserving cells (e.g., PUCCH towards the secondary base station). Thesecondary base station may determine which cell is the PSCell within theSCG. The master base station may not change the content of the RRCconfiguration provided by the secondary base station. If an SCG is addedand/or an SCG SCell is added, the master base station may provide thelatest measurement results for the SCG cell(s). Either or both of amaster base station and a secondary base station may know the SFN andsubframe offset of each other by OAM, (e.g., for the purpose of DRXalignment and identification of a measurement gap). If a new SCG SCellis added, dedicated RRC signaling may be used for sending requiredsystem information of the cell, such as for CA, except, e.g., for theSFN acquired from an MIB of the PSCell of an SCG.

FIG. 13A and FIG. 13B show examples for gNB deployment scenarios. A core1301 and a core 1310, in FIG. 13A and FIG. 13B, respectively, mayinterface with other nodes via RAN-CN interfaces. In a non-centralizeddeployment scenario in FIG. 13A, the full protocol stack (e.g., NR RRC,NR PDCP, NR RLC, NR MAC, and NR PHY) may be supported at one node, suchas a gNB 1302, a gNB 1303, and/or an eLTE eNB or LTE eNB 1304. Thesenodes (e.g., the gNB 1302, the gNB 1303, and the eLTE eNB or LTE eNB1304) may interface with one of more of each other via a respectiveinter-BS interface. In the centralized deployment scenario in FIG. 13B,upper layers of a gNB may be located in a Central Unit (CU) 1311, andlower layers of the gNB may be located in Distributed Units (DU) 1312,1313, and 1314. The CU-DU interface (e.g., Fs interface) connecting CU1311 and DUs 1312, 1312, and 1314 may be ideal or non-ideal. The Fs-Cmay provide a control plane connection over the Fs interface, and theFs-U may provide a user plane connection over the Fs interface. In thecentralized deployment, different functional split options between theCU 1311 and the DUs 1312, 1313, and 1314 may be possible by locatingdifferent protocol layers (e.g., RAN functions) in the CU 1311 and inthe DU 1312, 1313, and 1314. The functional split may supportflexibility to move the RAN functions between the CU 1311 and the DUs1312, 1313, and 1314 depending on service requirements and/or networkenvironments. The functional split option may change during operationafter the Fs interface setup procedure, or the functional split optionmay change only in the Fs setup procedure (e.g., the functional splitoption may be static during operation after Fs setup procedure).

FIG. 14 shows examples for different functional split options of acentralized gNB deployment scenario. Element numerals that are followedby “A” or “B” designations in FIG. 14 may represent the same elements indifferent traffic flows, e.g., either receiving data (e.g., data 1402A)or sending data (e.g., 1402B). In the split option example 1, an NR RRC1401 may be in a CU, and an NR PDCP 1403, an NR RLC (e.g., comprising aHigh NR RLC 1404 and/or a Low NR RLC 1405), an NR MAC (e.g., comprisinga High NR MAC 1406 and/or a Low NR MAC 1407), an NR PHY (e.g.,comprising a High NR PHY 1408 and/or a LOW NR PHY 1409), and an RF 1410may be in a DU. In the split option example 2, the NR RRC 1401 and theNR PDCP 1403 may be in a CU, and the NR RLC, the NR MAC, the NR PHY, andthe RF 1410 may be in a DU. In the split option example 3, the NR RRC1401, the NR PDCP 1403, and a partial function of the NR RLC (e.g., theHigh NR RLC 1404) may be in a CU, and the other partial function of theNR RLC (e.g., the Low NR RLC 1405), the NR MAC, the NR PHY, and the RF1410 may be in a DU. In the split option example 4, the NR RRC 1401, theNR PDCP 1403, and the NR RLC may be in a CU, and the NR MAC, the NR PHY,and the RF 1410 may be in a DU. In the split option example 5, the NRRRC 1401, the NR PDCP 1403, the NR RLC, and a partial function of the NRMAC (e.g., the High NR MAC 1406) may be in a CU, and the other partialfunction of the NR MAC (e.g., the Low NR MAC 1407), the NR PHY, and theRF 1410 may be in a DU. In the split option example 6, the NR RRC 1401,the NR PDCP 1403, the NR RLC, and the NR MAC may be in CU, and the NRPHY and the RF 1410 may be in a DU. In the split option example 7, theNR RRC 1401, the NR PDCP 1403, the NR RLC, the NR MAC, and a partialfunction of the NR PHY (e.g., the High NR PHY 1408) may be in a CU, andthe other partial function of the NR PHY (e.g., the Low NR PHY 1409) andthe RF 1410 may be in a DU. In the split option example 8, the NR RRC1401, the NR PDCP 1403, the NR RLC, the NR MAC, and the NR PHY may be ina CU, and the RF 1410 may be in a DU.

The functional split may be configured per CU, per DU, per UE, perbearer, per slice, and/or with other granularities. In a per CU split, aCU may have a fixed split, and DUs may be configured to match the splitoption of the CU. In a per DU split, each DU may be configured with adifferent split, and a CU may provide different split options fordifferent DUs. In a per UE split, a gNB (e.g., a CU and a DU) mayprovide different split options for different UEs. In a per bearersplit, different split options may be utilized for different bearertypes. In a per slice splice, different split options may be applied fordifferent slices.

A new radio access network (new RAN) may support different networkslices, which may allow differentiated treatment customized to supportdifferent service requirements with end to end scope. The new RAN mayprovide a differentiated handling of traffic for different networkslices that may be pre-configured, and the new RAN may allow a singleRAN node to support multiple slices. The new RAN may support selectionof a RAN part for a given network slice, e.g., by one or more sliceID(s) or NSSAI(s) provided by a UE or provided by an NGC (e.g., an NGCP). The slice ID(s) or NSSAI(s) may identify one or more ofpre-configured network slices in a PLMN. For an initial attach, a UE mayprovide a slice ID and/or an NSSAI, and a RAN node (e.g., a gNB) may usethe slice ID or the NSSAI for routing an initial NAS signaling to an NGCcontrol plane function (e.g., an NG CP). If a UE does not provide anyslice ID or NSSAI, a RAN node may send a NAS signaling to a default NGCcontrol plane function. For subsequent accesses, the UE may provide atemporary ID for a slice identification, which may be assigned by theNGC control plane function, to enable a RAN node to route the NASmessage to a relevant NGC control plane function. The new RAN maysupport resource isolation between slices. When the RAN resourceisolation is implemented, shortage of shared resources in one slice doesnot cause a break in a service level agreement for another slice.

The amount of data traffic carried over networks is expected to increasefor many years to come. The number of users/devices is increasing andeach user/device accesses an increasing number and variety of services,e.g., video delivery, large files, and images. This requires not onlyhigh capacity in the network, but also provisioning very high data ratesto meet customers' expectations on interactivity and responsiveness.More spectrum may be required for network operators to meet theincreasing demand Considering user expectations of high data rates alongwith seamless mobility, it is beneficial that more spectrum be madeavailable for deploying macro cells as well as small cells forcommunication systems.

Striving to meet the market demands, there has been increasing interestfrom operators in deploying some complementary access utilizingunlicensed spectrum to meet the traffic growth. This is exemplified bythe large number of operator-deployed Wi-Fi networks and the 3GPPstandardization of LTE/WLAN interworking solutions. This interestindicates that unlicensed spectrum, when present, may be an effectivecomplement to licensed spectrum for network operators, e.g., to helpaddress the traffic explosion in some scenarios, such as hotspot areas.Licensed Assisted Access (LAA) offers an alternative for operators tomake use of unlicensed spectrum while managing one radio network,offering new possibilities for optimizing the network's efficiency.

Listen-before-talk (clear channel assessment) may be implemented fortransmission in an LAA cell. In a listen-before-talk (LBT) procedure,equipment may apply a clear channel assessment (CCA) check before usingthe channel. For example, the CCA may utilize at least energy detectionto determine the presence or absence of other signals on a channel inorder to determine if a channel is occupied or clear, respectively. Forexample, European and Japanese regulations mandate the usage of LBT inthe unlicensed bands. Apart from regulatory requirements, carriersensing via LBT may be one way for fair sharing of the unlicensedspectrum.

Discontinuous transmission on an unlicensed carrier with limited maximumtransmission duration may be enabled. Some of these functions may besupported by one or more signals to be transmitted from the beginning ofa discontinuous LAA downlink transmission. Channel reservation may beenabled by the transmission of signals, by an LAA node, after gainingchannel access, e.g., via a successful LBT operation, so that othernodes that receive the transmitted signal with energy above a certainthreshold sense the channel to be occupied. Functions that may need tobe supported by one or more signals for LAA operation with discontinuousdownlink transmission may include one or more of the following:detection of the LAA downlink transmission (including cellidentification) by UEs, time synchronization of UEs, and frequencysynchronization of UEs.

DL LAA design may employ subframe boundary alignment according to LTE-Acarrier aggregation timing relationships across serving cells aggregatedby CA. This may not indicate that the eNB transmissions may start onlyat the subframe boundary. LAA may support transmitting PDSCH when notall OFDM symbols are available for transmission in a subframe accordingto LBT. Delivery of necessary control information for the PDSCH may alsobe supported.

LBT procedures may be employed for fair and friendly coexistence of LAAwith other operators and technologies operating in unlicensed spectrum.LBT procedures on a node attempting to transmit on a carrier inunlicensed spectrum may require the node to perform a clear channelassessment to determine if the channel is free for use. An LBT proceduremay involve at least energy detection to determine if the channel isbeing used. For example, regulatory requirements in some regions, e.g.,in Europe, specify an energy detection threshold such that if a nodereceives energy greater than this threshold, the node assumes that thechannel is not free. While nodes may follow such regulatoryrequirements, a node may optionally use a lower threshold for energydetection than that specified by regulatory requirements. In an example,LAA may employ a mechanism to adaptively change the energy detectionthreshold, e.g., LAA may employ a mechanism to adaptively lower theenergy detection threshold from an upper bound. Adaptation mechanism maynot preclude static or semi-static setting of the threshold. A Category4 LBT mechanism or other type of LBT mechanisms may be implemented.

Various example LBT mechanisms may be implemented. For some signals, insome implementation scenarios, in some situations, and/or in somefrequencies, no LBT procedure may performed by the transmitting entity.For example, Category 2 (e.g., LBT without random back-off) may beimplemented. The duration of time that the channel is sensed to be idlebefore the transmitting entity transmits may be deterministic. Forexample, Category 3 (e.g., LBT with random back-off with a contentionwindow of fixed size) may be implemented. The LBT procedure may have thefollowing procedure as one of its components. The transmitting entitymay draw a random number N within a contention window. The size of thecontention window may be specified by the minimum and maximum value ofN. The size of the contention window may be fixed. The random number Nmay be employed in the LBT procedure to determine the duration of timethat the channel is sensed to be idle before the transmitting entitytransmits on the channel. In an example, Category 4 (e.g., LBT withrandom back-off with a contention window of variable size) may beimplemented. The transmitting entity may draw a random number N within acontention window. The size of contention window may be specified by theminimum and maximum value of N. The transmitting entity may vary thesize of the contention window when drawing the random number N. Therandom number N may be used in the LBT procedure to determine theduration of time that the channel is sensed to be idle before thetransmitting entity transmits on the channel

LAA may employ uplink LBT at the UE. The UL LBT scheme may be differentfrom the DL LBT scheme, e.g., by using different LBT mechanisms orparameters. These differences in schemes may be due to the LAA UL beingbased on scheduled access, which may affect a UE's channel contentionopportunities. Other considerations motivating a different UL LBT schememay include, but are not limited to, multiplexing of multiple UEs in asingle subframe.

A DL transmission burst may be a continuous transmission from a DLtransmitting node, e.g., with no transmission immediately before orafter from the same node on the same CC. An UL transmission burst from aUE perspective may be a continuous transmission from a UE, e.g., with notransmission immediately before or after from the same UE on the sameCC. A UL transmission burst may be defined from a UE perspective or froman eNB perspective. If an eNB is operating DL and UL LAA over the sameunlicensed carrier, DL transmission burst(s) and UL transmissionburst(s) on LAA may be scheduled in a TDM manner over the sameunlicensed carrier. An instant in time may be part of a DL transmissionburst or part of an UL transmission burst.

Random access (RA) procedures may be used to establish communicationsbetween a wireless device and a base station in a cell. A four-step RAprocedure may include, e.g., a first step comprising a wireless devicesending, to a base station, a request to establish communications withthe base station. A second step may include, e.g., the base stationsending, to the wireless device, a response indicating that the wirelessdevice may send additional information for establishing the requestedcommunications. A third step may include, e.g., the wireless devicesending, to the base station, the additional information forestablishing the requested communications. A fourth step may include,e.g., the base station sending, to the wireless device, informationconfirming the establishing of the requested communications. A four-stepRA procedure may have an associated latency, e.g., which may be aminimum of fourteen transmission time intervals (TTI). As an example,3GPP TR 38.804 v14.0.0 indicates a minimum latency of fourteen TTIscomprising, e.g., 3 TTIs after a message from step 1 of a four-step RAprocedure, 1 TTI for a message from step 2 of a four-step RA procedure,5 TTIs after the message from step 2, 1 TTI for a message from step 3 ofa four-step RA procedure, 3 TTIs after the message from step 3, and 1TTI for a message from step 4 of a four-step procedure (e.g.,3+1+5+1+3+1=14). Reducing the number of steps in an RA procedure mayreduce latency. By using parallel transmissions, a four-step RAprocedure may be reduced to a two-step RA procedure. A two-step RAprocedure may have an associated latency, e.g., which may be a minimumof four TTIs and which may be less than an associated latency for afour-step RA procedure. As an example, 3GPP TR 38.804 v14.0.0 indicatesa minimum latency of four TTIs comprising, e.g., 3 TTIs after a messagefrom step 1 of a two-step RA procedure and 1 TTI for a message from step2 of a two-step RA procedure.

FIG. 15 shows examples of (a) a contention-based four-step RA procedure,(b) a contention free three-step RA procedure, (c) descriptions of acontention-based four-step RA procedure, and (d) a contention freetwo-step RA procedure. A four-step RA procedure may comprise a RAPtransmission in a first step, an RAR transmission in a second step, ascheduled transmission of one or more transport blocks (TBs) in a thirdstep, and contention resolution in a fourth step.

In step 1501, a base station may transmit four-step RA configurationparameters to a wireless device (e.g., a UE). The base station maygenerate and transmit RA configuration parameters periodically, e.g.,based on a timer. The base station may broadcast RA configurationparameters in one or more messages. The wireless device may perform aRAP selection process at step 1502, e.g., after receiving the four-stepRA configuration parameters. In a contention-based RA procedure, such asshown in part (a) of FIG. 15, the RA configuration parameters maycomprise a root sequence that may be used by the wireless device togenerate a RAP. The RAP may be randomly selected by the wireless device,among various RAP candidates generated by the root sequence, during theRAP selection process. The wireless device may perform the RAP selectionusing, e.g., the procedure described below regarding FIG. 16, and/or oneor more RAP selections procedures described herein.

During a first step of the RA procedure, at step 1503, a wireless devicemay transmit a RAP, e.g., using a configured RA preamble format with asingle particular transmission (Tx) beam. A random access channel (RACH)resource may be defined as a time-frequency resource to transmit a RAP.Broadcast system information may indicate whether wireless device shouldtransmit one preamble, or multiple or repeated preambles, within asubset of RACH resources.

In the second step of the four-step RA procedure, at step 1504, a basestation may transmit a random access response (RAR) to the wirelessdevice. The base station may transmit the RAR in response to an RAP thatthe wireless device may transmit. A wireless device may monitor thephysical-layer downlink control channel for RARs identified by theRA-RNTI in an RA response window. The RA response window may start at asubframe that contains the end of an RAP transmission, plus threesubframes, and the RA response window may have the lengthra-ResponseWindowSize. A wireless device may determine the RA-RNTIassociated with the PRACH in which the wireless device transmits an RAPby the following operation:RA-RNTI=1+t_id+10*f_id

where t_id is the index of the first subframe of the specified PRACH(0≤t_id<10), and f_id is the index of the specified PRACH within thatsubframe, in ascending order of frequency domain (0≤f_id≤6). Differenttypes of UEs, e.g., narrow band-Internet of Things (NB-IoT), bandwidthlimited (BL)-UE, and/or UE-Extended Coverage (UE-EC), may use differentformulas or operations for determining RA-RNTI. A base station mayconfigure an association between a DL signal or channel, a subset ofRACH resources, and/or a subset of RAP indexes. Such an association maybe for determining the DL transmission in the second step of the RAprocedure, at step 1504 of FIG. 15. Based on the DL measurement and thecorresponding association, a wireless device may select the subset ofRACH resources and/or the subset of RAP indexes.

In the third step of the four-step RA procedure (e.g., step 1505 in FIG.15), a wireless device may adjust an UL time alignment by using the TAvalue corresponding to the TA command in the received RAR in the secondstep (e.g., step 1504 in FIG. 15). A wireless device may transmit one ormore TBs to a base station using the UL resources assigned in the ULgrant in the received RAR. One or more TBs that a wireless device maytransmit in the third step (e.g., step 1505 in FIG. 15) may comprise RRCsignaling, such as an RRC connection request, an RRC connectionRe-establishment request, or an RRC connection resume request. The oneor more TBs may also comprise a wireless device identity, e.g., whichmay be used as part of the contention-resolution mechanism in the fourthstep (e.g., step 1506 in FIG. 15).

The fourth step in the four-step RA procedure (e.g., step 1506 in FIG.15) may comprise a DL message for contention resolution. Based on thesecond step (e.g., step 1504 in FIG. 15), one or more wireless devicesmay perform simultaneous RA attempts using the same RAP in the firststep (e.g., step 1503 in FIG. 15), and/or receive the same RAR with thesame TC-RNTI in the second step (e.g., step 1504 in FIG. 15). Thecontention resolution in the fourth step may be to ensure that awireless device does not incorrectly use another wireless deviceidentity. The contention resolution mechanism may be based on either aC-RNTI on a PDCCH, or a UE Contention Resolution Identity on a DL-SCH,e.g., depending on whether or not a wireless device has a C-RNTI. If awireless device has a C-RNTI, e.g., if the wireless device detects theC-RNTI on the PDCCH, the wireless device may determine the success of RAprocedure. If the wireless device does not have a C-RNTI (e.g., if aC-RNTI is not pre-assigned), the wireless device may monitor a DL-SCHassociated with a TC-RNTI, e.g., that a base station may transmit in anRAR of the second step. In the fourth step (e.g., step 1506 in FIG. 15),the wireless device may compare the identity in the data transmitted bythe base station on the DL-SCH with the identity that the wirelessdevice transmits in the third step (e.g., step 1505 in FIG. 15). If thewireless determines that two identities are the same or satisfy athreshold similarity, the wireless device may determine that the RAprocedure is successful. If the wireless device determines that the RAis successful, the wireless device may promote the TC-RNTI to theC-RNTI. A TC-RNTI may be an identifier initially assigned to a wirelessdevice when the wireless device first attempts to access a base station.A TC-RNTI may be used for a wireless device in an idle state. Afteraccess is allowed by the base station, a C-RNTI may be used foridentifying the wireless device. A C-RNTI may be used for a wirelessdevice in an inactive or an active state.

The fourth step in the four-step RA procedure (e.g., step 1506 in FIG.15) may allow HARQ retransmission. A wireless device may start amac-ContentionResolutionTimer when the wireless device transmits one ormore TBs to a base station in the third step (e.g., step 1505 in FIG.15). The wireless may restart the mac-ContentionResolution Timer at eachHARQ retransmission. When a wireless device receives data on the DLresources identified by C-RNTI or TC-RNTI in the fourth step (e.g., step1506 in FIG. 15), the wireless device may stop themac-ContentionResolution Timer. If the wireless device does not detectthe contention resolution identity that matches the identity transmittedby the wireless device in the third step (e.g., step 1505 in FIG. 15),the wireless device may determine that the RA procedure has failed andthe wireless device may discard the TC-RNTI. Additionally oralternatively, if the mac-ContentionResolutionTimer expires, thewireless device may determine that the RA procedure has failed and thewireless device may discard the TC-RNTI. If the wireless devicedetermines that the contention resolution has failed, the wirelessdevice may flush the HARQ buffer used for transmission of the MAC PDUand the wireless device may restart the four-step RA procedure from thefirst step (e.g., step 1503 in FIG. 15). The wireless device may delaysubsequent RAP transmission, e.g., by a backoff time. The backoff timemay be randomly selected, e.g., according to a uniform distributionbetween 0 and the backoff parameter value corresponding to the BI in theMAC PDU for RAR.

In a four-step RA procedure, the usage of the first two steps may be,e.g., to obtain a UL time alignment for a wireless device and/or toobtain an uplink grant. The UL time alignment may not be necessary inone or more scenarios. For example, in small cells, or for stationarywireless devices, the process for acquiring the UL time alignment maynot be necessary if either a TA equal to zero may be sufficient (e.g.,for small cells), or if a stored TA value from the last RA may be ableto serve for the current RA (e.g., a stationary wireless device). If awireless device is in an RRC connected state, e.g., with a valid TAvalue and no resource configured for UL transmission, the UL timealignment may not be necessary when the wireless device attempts toobtain an UL grant.

Part (b) of FIG. 15 shows a three-step contention free RA procedure. Abase station may transmit RA configuration parameters to a wirelessdevice, e.g., a UE, in step 1510. In a contention-free RA procedure,such as shown in part (b) of FIG. 15, the configuration parameters mayindicate to the wireless device what preamble to send to the basestation and when to send the preamble. The base station may alsotransmit a control command to the wireless device at step 1511. Thecontrol command may comprise, e.g., downlink control information. In afirst step of the RA procedure, the wireless device may transmit arandom access preamble transmission to the base station at step 1512.The RAP transmission may be based on the RA configuration parameters andthe control command. In a second step of the RA procedure, the basestation may transmit to the wireless device a random access response atstep 1513. In a third step of the RA procedure, the wireless device maytransmit scheduled transmissions at step 1514. The scheduledtransmissions may be based on the RAR. The contention free RA proceduremay end with the third step. Thereafter, the base station may transmit adownlink transmission to the wireless device at step 1515. This downlinktransmission may comprise, e.g., an acknowledgement (ACK) indication, anon-acknowledgement (NACK) indication, data, or other information.Contention-free RA procedures such as described above may have reducedlatency compared with contention-based RA procedures. Contention-basedRA procedures may involve collisions, such as when more than onewireless device is attempting to communicate with the same base stationat the same time.

Part (c) of FIG. 15 shows an example of common language descriptionsthat may facilitate an understanding of some of the messaging involvedin the contention-based four-step RA procedure described above regardingpart (a) of FIG. 15. In step 1 of the RA procedure, a wireless devicemay send a communication to a base station similar to a request such as,“Hello, can I camp on?” (step 1520). If the base station can accommodatethe wireless device request, the base station may respond to thewireless device with a message similar to an instruction such as “Sendyour info & data here” (step 1521). Based on the base station'sresponse, the wireless device may send a message similar to a responsesuch as “Here you are” (step 1522). Based on the information received bythe base station, the base station may respond with a message similar toa grant such as “You are now in” (step 1523).

Part (d) of FIG. 15 shows an example of a two-step contention freerandom access procedure of a wireless device. At step 1530, the wirelessdevice may receive RA configuration parameters from a base station(e.g., from a handover source base station, and/or from a handovertarget base station via the handover source base station). The RAconfiguration parameters may comprise one or more parameters indicatinga type of a random access process. The type of the random access processmay indicate a two-step random access process. At step 1531, thewireless device may transmit an RA preamble and one or more transportblocks as a first step of the procedure, e.g., overlapping in time witheach other. In response to the RA preamble and/or the one or moretransport blocks, at step 1532, the wireless device may receive an RAresponse from a base station (e.g., a handover target base station).

FIG. 16 shows an example of a RAP selection procedure for preamblegroups that may be used as the RAP selection process at step 1502 ofFIG. 15. A base station may broadcast the RAP grouping information,along with one or more thresholds, in system information. At step 1601,a wireless device may select a preamble group comprising preambles. Twoor more RAP groups may be indicated by broadcast system information, andone or more of the RAP groups may be optional. At step 1602, thewireless device may select a RAP group among a plurality of RAP groups,based on, e.g., a size of data that the wireless may have to transmit, ameasured pathloss, and/or other information. At step 1603, the wirelessdevice may generate a RAP from the selected RAP group. If a base stationconfigures two groups, e.g., in a four-step RA procedure, a wirelessdevice may use the pathloss and a size of the message transmitted by thewireless device in the third step of the RA procedure, to determine fromwhich group the wireless device selects an RAP. A base station may use agroup type to which a RAP belongs as an indication of the message sizein the third step and/or the radio conditions at a wireless device. Theprocess may end at step 1603.

FIG. 17 shows an example of a MAC PDU comprising a MAC header and MACRARs. A four-step RA procedure may use the arrangement shown in FIG. 17.A two-step RA procedure may also use the arrangement shown in FIG. 17.Additionally or alternatively, a two-step RA procedure may use avariation of the arrangement shown in FIG. 17, e.g., with additional orfewer fields, and/or with longer or shorter fields. If an RAR comprisesa RAPID corresponding to a RAP that a wireless device transmits, thewireless device may process the data in the RAR. The data in the RAR maycomprise, e.g., one or more of a timing advance (TA) command, a ULgrant, and/or a Temporary C-RNTI (TC-RNTI). The MAC header may comprisesubheaders, such as an E/T/R/R/BI subheader (described further below)and up to n number of E/T/RAPID subheaders (described further below).The E/T/R/R/BI subheader may comprise an octet of bits comprising 1 biteach of E, T, R, and R, and four bits of BI. Each of n E/T/RAPIDsubheaders may comprise an octet comprising 1 bit each of E and T, and 6bits of an RAPID.

FIG. 18 shows an example of an uplink resource 1801 that may be used,e.g., for a transmission of a random access preamble and data in a firststep of a two-step RA procedure. A transmission may comprise a randomaccess preamble 1803, e.g., via a physical random access channel(PRACH), and data 1802. The data 1802 may comprise one or more transportblocks, an identifier of a wireless device, and/or other information.The data may be included in, e.g., an RRC connection request. The RRCconnection request may comprise one or more of, e.g., the data 1802, anidentifier of a wireless device, an indication of a type of data (e.g.,emergency, high priority access, standard access, signaling, etc.),and/or other information. The RAP 1803 may comprise a preamble sequence,e.g., bits arranged in octets 1804. A guard time and/or a cyclic prefixmay be inserted, e.g., at either end of the preamble sequence.Additionally or alternatively, a guard band may be inserted above thepreamble sequence and/or below the preamble sequence.

FIG. 19 shows examples of MAC RAR formats comprising a TA command, a ULGrant, and a TC-RNTI for a four-step RA procedure. Part (a) shows anexample MAC RAR format, part (b) shows an example MAC RAR for a PRACHenhanced coverage level 2 or level 3, and part (c) shows an example MACRAR for NB-IoT UEs.

In FIG. 19 part (a), a first octet comprises 1 bit of R, and 7 bits ofthe TA command. The second octet comprises an additional 4 bits of theTA command as well as 4 bits of the UL grant. The third and fourth octeteach comprise 8 additional bits of the UL grant. And, the fifth andsixth octet each comprise 8 bits of the TC-RNTI. In FIG. 19 part (b),the MAC RAR for PRACH enhanced coverage level 2 or level 3 comprises aMAC RAR similar to the MAC RAR example in FIG. 19 part (a), except thatin part (b) the UL grant comprises 8 bits in the third octet and theTC-RNTI is included in the fourth and fifth octets. In FIG. 19 part (c),a MAC RAR example for NB-IoT UEs comprises a MAC RAR similar to the MACRAR in FIG. 19 part (a), except that the fourth octet in part (c)comprises 3 bits of the UL grant and 5 bits of R. As shown in FIG. 19parts (a), (b), and (c), a MAC RAR may comprise one or more reservedbits (R bits). One or more of the R bits in the MAC RAR may indicatewhether a RA procedure is a 2-step RA procedure or a 4-step RAprocedure.

FIG. 20 shows a two-step RA procedure that may comprise an uplink (UL)transmission of an RAP and data, followed by a downlink (DL)transmission of an RAR and contention resolution information. A two-stepRA procedure may reduce RA latency compared with a four-step RA process,e.g., by integrating a process to obtain a timing advance (TA) valuewith a data transmission. In the UL transmission of a two-step RAprocedure at step 2003, a wireless device may transmit, via a cell andto a base station, a RAP for UL time alignment and/or an UL message. TheUL message may comprise, e.g., an UL grant, a wireless device ID, one ormore TBs, a C-RNTI, and/or other information. In the DL transmission atstep 2004, a base station may transmit an RAR and contention resolutioninformation. The DL transmission may identify an assignment of dedicatedresources for the wireless to transmit data, e.g., which may include anassignment of one or more transport blocks. The DL transmission may bein response to the UL transmission. The RAR may comprise anacknowledgement of a reception of the one or more transport blocks,and/or an indication of a successful decoding of the one or moretransport blocks. The contention resolution may comprise, e.g., TAinformation, an UL grant, a C-RNTI, and/or a contention resolutionidentity.

In the UL transmission of a two-step RA procedure, a wireless device,may transmit, via a cell and to a base station, an RAP in parallel withone or more TBs. The wireless device may acquire one or moreconfiguration parameters for the UL transmission before the wirelessdevice starts a two-step RA procedure, e.g., at step 2001. In acontention-based RA procedure such as shown in FIG. 20, the one or moreconfiguration parameters may comprise a root sequence that may be usedby the wireless device to generate an RAP. The wireless device maydetermine an RAP at step 2002. An RAP selection by the wireless devicemay be based on the RA configuration parameters received at step 2001,e.g., comprising one or more RAP selections procedures described herein.The wireless device may use the root sequence to generate one or morecandidate preambles, and the wireless device may randomly select one ofthe candidate preambles as the RAP. The one or more candidate preamblesmay be organized into groups that may indicate an amount of data fortransmission. For example a first group may comprise RAPs indicated forsmall data transmissions, and a second group may comprise RAPs indicatedfor larger data transmissions. By transmitting an RAP from a specificgroup of RAPs, the wireless device may be able to indicate a size ofdata it may have for transmission. The wireless device may transmit theRAP via a RACH resource. The wireless device may transmit the one ormore TBs via an UL resource associated with the RAP. The ULtransmissions may occur, e.g., in the same subframe, in consecutivesubframes, or in the same burst. A two-step RA procedure may be on acontention basis. The contention may occur for the RAP and/or datatransmission.

In the UL transmission, the RAP may be used to adjust UL time alignmentfor a cell and/or to aid in channel estimation for one or more TBs. Aportion of the UL transmission for one or more TBs may comprise, e.g., awireless device ID, a C-RNTI, a service request such as buffer statereporting (e.g., a buffer status report) (BSR), one or more user datapackets, and/or other information. A wireless device in an RRC connectedstate may use a C-RNTI as an identifier of the wireless device (e.g., awireless device ID). A wireless device in an RRC inactive state may usea C-RNTI (if available), a resume ID, or a short MAC-ID as an identifierof the wireless device. A wireless device in an RRC idle state may use aC-RNTI (if available), a resume ID, a short MAC-ID, an IMSI(International Mobile Subscriber Identifier), a T-IMSI (Temporary-IMSI),and/or a random number as an identifier of the wireless device.

The UL transmission may comprise one or more TBs that may be transmittedusing a two-step RA procedure different ways. User data packet(s) may bemultiplexed in the first step of a two-step RA procedure. A base stationmay configure one or more resources reserved for the UL transmissionthat may be indicated to a wireless device before the UL transmission.If the wireless device transmits one or more TBs in the first step ofthe two-step RA procedure, a base station may transmit in a DLtransmission an RAR that may comprise a contention resolution messageand/or an acknowledgement/non-acknowledgement message of the UL datatransmission. The DL transmission may be in response to the ULtransmission. A wireless device may transmit one or more TBs after thereception of an RAR. The wireless device may transmit an indicator, suchas buffer state reporting, in the UL transmission. The indicator mayindicate to a base station an amount of data the wireless device mayattempt to transmit. The base station may assign a UL grant based on theindicator. The base station may transmit the UL grant to the wirelessdevice via an RAR. If UL data transmission, based on the UL grant via anRAR, occurs after the reception of RAR, the UL data transmission mayoccur on a contention-based channel. The UL data transmission may occurafter a wireless device receives the RAR, e.g., in a subframe x+5, orx+n, where x is a subframe in which the RAR is received by the wirelessdevice and n is any whole number greater than zero.

A wireless device may provide, to a base station, an indication of arequired UL grant size. The wireless device may provide this indication,e.g., by determining a RAP selection (e.g., at step 2002), as opposed totransmitting a BSR, e.g., comprising one or more RAP selectionsprocedures described herein. A base station may partition RAPs availableto the base station into one or more RAP groups such that each partitionmay indicate a particular UL grant size. A wireless device may indicatea request, to a base station, of a small or large grant by selecting aRAP from a designated group. The base station may determine therequested grant size based on a RAP that the base station receives. Abase station may configure an association between RAP groups and a ULgrant size. The base station may broadcast one or more parameters viasystem information to indicate the association between RAP groups and aUL grant size.

A wireless device may provide, to a base station, an indication of arequired UL grant size by transmitting an RAP on a partitioned radioresource. A base station may partition radio resources used for RAPtransmission into one or more groups such that one or more resources ina group carrying an RAP may indicate a UL grant size that a wirelessdevice may request. The base station may determine the requested grantsize based on a RAP received by the base station via resources in agroup. When a high granularity is required, a base station may configurea large number of radio resources for the RAP transmission. A basestation may configure an association between radio resource groups and aUL grant size. The base station may broadcast one or more parameters viasystem information to indicate the association between radio resourcegroups and a UL grant size.

In the second step of the two-step RA procedure (e.g., step 2004), abase station may transmit an RAR to a wireless device. The base stationmay transmit the RAR in response to receiving the RAP and data from thewireless device. The RAR may comprise TA information, a contentionresolution identity, a UL grant, and/or a C-RNTI. A MAC PDU may compriseone or more of an RAR MAC subheader and a corresponding RAR. The TA maybe used by the wireless device for a two-step RA procedure, e.g., when aTA timer has expired.

A base station may or may not transmit the contention resolutionidentity to a wireless device. If a wireless device transmits a C-RNTI(e.g., as a wireless device ID) in a UL transmission, the wirelessdevice may complete contention resolution based on a C-RNTI in an RAR.If a wireless device transmits a shared RNTI, that may be monitored bymore than one wireless device as a wireless device ID in a ULtransmission, the wireless device may complete contention resolutionbased on a contention resolution identity in an RAR. Other identifiersfor a wireless device, such as a random number, resume ID, T-IMSI,and/or IMSI may be used to complete the contention resolution.

The UL grant may be for a wireless device that may have subsequent ULdata to transmit. BSR may be transmitted by a wireless device in the ULtransmission. A base station may use the BSR for determining a UL grant.

A wireless device may not have a C-RNTI, such as a wireless device in anRRC inactive state. If a two-step RA procedure is used for statetransition from inactive to connected, a base station may assign aC-RNTI to a wireless device that lacks a C-RNTI.

A wireless device may acquire one or more two-step RA configurationparameters (e.g., in step 2001 of FIG. 20) from one or more messagesbroadcast and/or unicast by a cell. A base station may broadcast ormulticast, via a cell, one or more two-step RA configuration parameterscomprised in one or more system information blocks. The base station maytransmit configuration parameters to a wireless device via dedicatedresource(s) and signaling, such as via a unicast to a wireless device inan RRC connected state.

A base station may configure or restrict the usage of the two-step RAprocedure to one or more case-based procedures, services, or radioconditions. If a cell is small such that there may be no need for a TA,a base station in the cell may use broadcast signaling to configure allwireless devices under its coverage to use a two-step RA procedure. Awireless device may acquire the configuration, via one or more systeminformation blocks, and/or via L1 control signaling used to initiate atwo-step RA procedure for downlink data arrival.

If a base station has macro coverage, a wireless device having a storedand/or persisted TA value, e.g., a stationary or near stationarywireless device such as a sensor-type wireless device, may perform atwo-step RA procedure. A base station having macro coverage may usededicated signaling to configure a two-step RA procedure with one ormore wireless devices having stored and/or persisted TA values under thecoverage.

A wireless device in an RRC connected state may perform a two-step RAprocedure, e.g., when performing a network initiated handover, and/orwhen the wireless device requires or requests a UL grant within arequired delay and there are no physical-layer uplink control channelresources available to transmit a scheduling request. A wireless devicein an RRC inactive state may perform a two-step RA procedure, e.g., fora small data transmission while remaining in the inactive state or forresuming a connection. A wireless device may initiate a two-step RAprocedure, for example, for initial access such as establishing a radiolink, re-establishment of a radio link, handover, establishment of ULsynchronization, and/or a scheduling request when there is no UL grant.

Determining a type of RA procedure may comprise determining whether todo a 2-step or a 4-step RA procedure. An indicator may be provided in aMAC PDU subheader. Such an indicator may be included in a RAP identifier(RAPID), such as shown in FIG. 17. A RAPID may identify a specific RAP,where up to 2^(n) unique RAPs are possible for an n-bit wide RAPID.Multiple wireless devices may transmit their own RAPs to a base station.A base station may receive RAPs from a plurality of wireless devices.Each RAPID may indicate one of the plurality of RAPs transmitted to abase station. A wireless device may determine a RAP. This determinationmay be performed by the wireless device using a random process. Thewireless device may transmit the RAP. If a base station detects the RAPfrom the wireless device, the base station may use bits in a RAPID fieldto identify that RAP. The base station may transmit the RAPID in a MACsubheader within a MAC header of a MAC PDU, such as shown in FIG. 17.The wireless device that transmits the RAP may receive a MAC PDUcomprising the RAPID in a MAC subheader. The wireless device maydetermine, based on the RAPID, that the RAP was successfully received bythe base station.

The number of n bits in a RAPID may be 6 bits, such as in the RAPIDshown in FIG. 17, or any number of bits greater or smaller than 6. Thebase station may determine an estimate of a number of wireless devicessupported in a cell. The base station may also determine, based on theestimated number of wireless devices in a cell, a total number of RAPsthat may be used for the cell. The base station may also determine,based on the number of RAPs that may be used for the cell, the number ofbits to be used in the RAPID for identifying a RAP. The base station mayreduce the number of bits used in the RAPID for identifying unique RAPs,which in turn, may allow one or more bits of the RAPID shown in FIG. 17,to be used for other information, such as a type of RA procedure to beused. Using fewer than n bits for identifying RAPs, may allow use of oneor more unused RAPID bits as an indicator for other information such aswhether a random access procedure uses a 2-step procedure or a 4-stepprocedure. The indication of whether a RA procedure is 2-steps or4-steps may be in the form of a single bit, where “0” indicates one ofthe two possible RA procedures, such as a 2-step procedure, and “1”indicates the other, such as a 4-step procedure. Additionally oralternatively, more than one bit of a RAPID may be used, e.g., 2 or 3bits, to indicate additional information, such as information specificto one or more steps in a RA procedure.

One or more bits of the E and/or T fields, such as in a MAC subheadercomprising a RAPID shown in FIG. 17, may be used as an indication of atype of RA procedure, such as a 2-step RA procedure or a 4-step RAprocedure. The E field may be an extension field. A MAC subheader withan E field set to 1 may indicate the presence of a backoff indicator(BI) in the subheader and the presence of an additional MAC subheader. AMAC subheader with an E field set to 0 may indicate the presence of aRAPID in the subheader. The T field may be an indication of a presenceof additional MAC subheaders. A MAC subheader with a T field set to 1may indicate the presence of an additional MAC subheader, and a MACsubheader with a T field set to 0 may indicate that the MAC subheader isthe last MAC subheader in the MAC header. One or more of these E and/orT fields may be used to indicate a type of RA procedure, such as a2-step RA procedure or a 4-step RA procedure.

A wireless device may perform a method for determining whether toperform a 2-step RA procedure or a 4-step RA procedure. The wirelessdevice may transmit, to a base station, a RAP comprising a RAPidentifier (e.g., RAPID/RAP ID) and one or more transport blocks.Additionally or alternatively, the wireless device may transmit, to abase station, one or more preambles in parallel with one or moretransport blocks. Any of the above transmissions by the wireless devicemay be based on a determination, by the wireless device, that the typeof the RA procedure is a two-step RA procedure. The wireless device mayreceive, from the base station, a MAC PDU comprising one or more MACsubheaders and one or more MAC RARs, such as shown in FIG. 17. Thistransmission by base station may be based on the first transmission bythe wireless device. Each of the RARs may be associated with one of theone or more MAC subheaders. The wireless device may determine, based ona first field in a particular MAC subheader of the one or more MACsubheaders, a type of an RA procedure. Additionally or alternatively,based on the type of RA procedure (e.g., based on the first field in theparticular MAC subheader), the wireless device may determine a size ofan RAR that is associated with the particular MAC subheader comprisingthe field (e.g., a first MAC subheader, a second MAC subheader, etc.).The type of RA procedure may be, e.g., either a 2-step RA procedure or a4-step RA procedure. Additionally or alternatively, the RA procedure maybe a 3-step RA procedure, or some other number of steps. This particularMAC subheader may comprise a second field comprising the first fieldand/or one or more bits of an RAP identifier (e.g., a RAPID/RAP ID).This particular MAC subheader may also comprise an extension field, atype field, and/or a reserved bit. The wireless device may determine,based on a comparison of the field in the particular MAC subheader withthe RAPID of the RAP transmitted by the wireless device, whether the RAPin the first transmission by the wireless device is successfullyreceived by the base station. The wireless device may determine the typeof RA procedure (e.g., a two-step RA procedure) based on whether aninitial attempt of the particular RA procedure is successful. If thewireless device determines that the first attempt at the RA procedure isnot successful, the wireless device may retransmit the firsttransmission and/or the wireless device may determine to perform afour-step RA procedure, such as shown in FIG. 15 part (a) and describedabove. The wireless device may determine whether a random process hascompleted. This determining whether a random access has completed may bebased on, e.g., the first MAC subheader comprising a random accesspreamble identifier of the one or more preambles, and/or a second fieldin the first RAR that indicates that the one or more transport blockshave been successfully received by the base station. Additionally oralternatively, the determining that the random access procedure hascompleted may be based on the type of the random access procedure of thefirst RAR being a two-step random access procedure. The wireless devicemay transmit, based on a second field in the first RAR that indicatesthat at least one of the one or more transport blocks have not beensuccessfully received by the base station, one or more messages using afour-step random access procedure. The wireless device may receive, froma base station, one or more messages comprising configuration parametersof a two-step random access procedure and/or configuration parameters ofa four-step random access procedure. The wireless device may receive,from the base station, an RAR that may comprise an uplink grant. Thewireless device may retransmit, in response to a field of the RAR (e.g.,a first field, a second field, etc.) indicating that one or moretransport blocks have not been successfully received by the basestation, the one or more transport blocks. A wireless device may performany combination of one or more of the above steps. A base station, orany other device, may perform any combination of a step, or acomplementary step, of one or more of the above steps.

A base station may perform a method for determining whether to perform atwo-step RA procedure or a four-step RA procedure. The base station mayreceive, from a wireless device, an RAP. The base station may alsoreceive, in this first transmission from the wireless device, one ormore transport blocks. The base station may determine, based on the RAP,a type of RA procedure. The type of RA procedure may be, e.g., either atwo-step RA procedure or a four-step RA procedure. Additionally oralternatively, the RA procedure may be a 3-step RA procedure, or someother number of steps. The base station may transmit, to the wirelessdevice and based on the RAP, a MAC PDU comprising one or more MACsubheaders and one or more MAC RARs, such as shown in FIG. 17. Aparticular MAC subheader may comprise a field indicating the type of theRA procedure. This particular MAC subheader may comprise one or morebits of an RAP identifier (e.g., a RAPID/RAP ID). This particularsubheader may also comprise an extension field, a type field, and/or areserved bit. Each of the one or more RARs may be associated with one ofthe one or more MAC subheaders. The RAR may comprise the same size orone of a plurality of different sizes. An indication of the type of theRA procedure may be based on a RAPID in the RAP. Additionally oralternatively, an indication of the type of the RA procedure may bebased on one or more of the extension field, the type field, and/or areserved bit. A base station may perform any combination of one or moreof the above steps. A wireless device, or any other device, may performany combination of a step, or a complementary step, of one or more ofthe above steps.

A base station may determine a first MAC PDU for a two-step RA procedurecomprising RARs only for two-step RA procedures, and a base station maydetermine a second and different MAC PDU for a 4-step RA procedurecomprising RARs only for 4-step RA procedures, wherein each RAR in a MACPDU is for the same type of RA procedure. The base station may providean indicator as to which type of RA procedure the MAC PDU corresponds.Such an indicator may be included in any location of the MAC PDU, e.g.,within a MAC header or within MAC RARs (e.g., within an R fieldcomprising reserved bits). By including the indicator in the MAC header,a wireless device may be able to determine the type of RA procedure, aswell as the size of the MAC RARs, prior to receiving or decoding the MACRARs of the MAC PDU.

A base station may multiplex different type of RA responses (RARs) intoone MAC PDU. A wireless device may require or request resources for bothtwo-step RA and four-step RA procedures, and these resources fordifference types of RA procedures may be independent of each other. Abase station may require or request to use additional resources toaccommodate a MAC PDU for 2-step RA procedures that may be differentfrom a MAC PDU for 4-step procedures. If a base station multiplexes twotypes of RARs (e.g., RARs for 2-step RA procedures and RARs for 4-stepRA procedures) into one MAC PDU, the base station may only be able toassign common RACH resources, where a UE can transmit a 2-step RAP or a4-step RAP. Resources in the uplink and the downlink may be conserved byidentifying an RA type without allocating separate resources fordifferent MAC PDUs. If a base station multiplexes two types of RARs inthe same MAC PDU, e.g., if the length of a two-step RAR may be differentthan the length of a four-step RAR, one or more indicators may berequired to indicate one or more RAR boundaries in the same MAC PDU.

A base station may determine a type of RA procedure, such as a two-stepRA procedure or a four-step RA procedure, for communications with one ormore wireless devices. A base station may monitor RACH resources todetermine whether one or more RAPs are received. If a RAP is received,the base station may determine a type of RA procedure for the RAP, suchas a two-step RA procedure or a four-step RA procedure. The base stationmay determine, based on the type of the RA procedure for the RAP, acorresponding type of RA procedure for communications with the wirelessdevice that transmitted the RAP. The base station may make the abovedeterminations for a plurality of RAPs, and each of the plurality ofRAPs may be associated with one of a plurality of wireless devices. Thebase station may multiplex a plurality of MAC PDUs. Each of the MAC PDUsmay comprise a one or more MAC subheaders. At least one of the one ormore MAC subheaders may comprise an indication of a type of an RAprocedure, such as a two-step RA procedure or a four-step RA procedure.The base station may transmit the multiplexed plurality of MAC PDUs. Oneor more of the plurality of wireless devices may receive the multiplexedMAC PDUs and determine whether to perform one or more steps of an RAprocedure with the base station. The one or more of the plurality ofwireless devices may determine, based on one or more indications in aMAC subheader of at least one of the MAC PDUs, a type of the RAprocedure for communications with the base station.

A base station and/or a wireless device may determine whether an attemptfor an RA procedure is successful. If an attempt for an RA procedure issuccessful, the base station and the wireless device may communicateusing the type of RA procedure of the successful attempt. If the attemptfor an RA procedure is not successful, the base station and/or thewireless device may make another attempt for an RA procedure of the sametype as the prior attempt. If one or more attempts (e.g., up to athreshold number) for an RA procedure of a particular type of RAprocedure (e.g., a two-step RA procedure) are not successful, the basestation and/or the wireless device may attempt an RA procedure of adifferent type (e.g., a four-step RA procedure). A base station mayperform any combination of one or more of the above steps. A wirelessdevice, or any other device, may perform any combination of a step, or acomplementary step, of one or more of the above steps.

A two-step RA procedure may be attempted by a wireless device. Thewireless device may transmit, to a base station, an RAP in parallel withdata. The data may be an uplink message that may comprise, e.g., anidentifier of the wireless device and other data such as one or moretransport blocks. A base station may receive the transmission from thewireless device and the base station may decode one or more transportblocks received from the wireless device. The base station may transmit,to the wireless device, a random access response (RAR). The base stationmay include the RAR in a MAC PDU. The base station may also include oneor more additional RARs in the MAC PDU. The base station may multiplexthe MAC PDU with other MAC PDUs. The base station may transmit themultiplexed MAC PDUs. The base station may include in the RAR, which maybe responsive to the first transmission of the wireless device, one ormore indications of whether the one or more transport blocks weresuccessfully received by the base station. The one or more indicationsmay be included in one or more R fields of one or more reserved bits ofthe RAR. Examples of R fields are shown, e.g., as “R” in FIG. 19 parts(a), (b), and (c). The wireless device may receive the multiplexed MACPDUs. The wireless device may demultiplex the multiplexed MAC PDUs. Thewireless device may determine, based on a RAPID or other indication in aMAC subheader of a MAC PDU, that a particular RAR associated with thatMAC subheader is intended for the wireless device. For example, if aRAPID in a MAC subheader of a MAC PDU corresponds to an RAP that awireless device transmitted to a base station, the wireless device maydetermine that a particular RAR associated with that MAC subheadercomprising the RAPID is intended for the wireless device. The RAPID orother indication in the MAC subheader may include an indication of theidentifier of the wireless device that was previously included in theuplink message of the transmission by the wireless device. The wirelessdevice may determine, based on the indication in the RAR associated withthe MAC subheader, whether the one or more transport blocks weresuccessfully received by the base station. As described above, theindication may comprise one or more bits in one or more R fields in theRAR. R fields may comprise remainder bits of an octet comprising fieldsdesignated for other purposes, and these remainder bits may be reservedfor future use or for one or more indications such as described above.An indication whether one or more transport blocks were successfullyreceived by the base station may comprise a single bit. The indicationmay also comprise one or more additional bits to provide additionalinformation to the wireless device. The additional information providedby one or more additional bits may comprise, e.g., a redundancy versionfor a retransmission of one or more transport blocks by the wirelessdevice.

A wireless device may perform a method for determining whether a 2-stepRA procedure is successful. A wireless device may receive, from a basestation, one or more messages comprising configuration parameters for aRACH of a cell. The configuration parameters may comprise one or more RAparameters. The wireless device may transmit, to the base station, anRAP in parallel with: one or more first TBs with a first redundancyversion (RV) associated with a HARQ process. This first transmission bythe wireless device may be based on the one or more RA parameters. Theone or more first TBs may comprise an identifier associated with thewireless device (e.g., UE ID). The wireless device may receive, from thebase station, an RAR MAC PDU comprising, e.g., a preamble identifier(e.g., RAPID), an uplink grant, a field indicating whether the one ormore first TBs are successfully received by a base station, and/or anRNTI. The RNTI may comprise, e.g., one or more of a C-RNTI or a TC-RNTI.The uplink grant may comprise an indication of uplink resources. Thefield indicating whether the one or more first TBs are successfullyreceived by the base station may comprise: one or more of the identifierassociated with the wireless device or a C-RNTI, if the one or morefirst TBs are received successfully by the base station; or one or moreof a fixed value or a TC-RNTI, if the one or more first TBs are notreceived successfully by the base station. One or more transport blocksmay be considered successfully received by the base station if the basestation is able to decode information contained in the one or moretransport blocks. Additionally or alternatively, the RAR MAC PDU maycomprise at least one MAC subheader that comprises one or more of aTC-RNTI or an indication of a decoding failure. The wireless device maytransmit, to the base station, one or more first TBs with a second RVassociated with the HARQ process, wherein the second RV may be the sameas/or different from the first RV. The wireless device may receive, fromthe base station, a downlink packet comprising the identifier associatedwith the wireless device, if the one or more first TBs with the first RVor the second RV are received successfully by the base station. Thewireless device may receive, from the base station, an indication of aNACK, if TBs are not received successfully. The wireless device maytransmit, based on the indication of the NACK, a HARQ comprisingretransmitted TBs with another RV different from the prior first andsecond RVs. The wireless device may receive, from the base station, anindication of an ACK, if TBs are successfully received. If the one ormore first TBs are not received successfully by the base station, thewireless device may determine that the RA procedure has failed and/orthe wireless device may fall back to a four-step RA procedure, such asdescribed above regarding FIG. 15 part (a). A wireless device mayperform any combination of one or more of the above steps. A basestation, or any other device, may perform any combination of a step, ora complementary step, of one or more of the above steps.

A base station may perform a method for determining whether a two-stepRA procedure is successful. A base station may transmit, to a wirelessdevice, one or more messages comprising configuration parameters for aRACH of a cell. The configuration parameters may comprise one or more RAparameters. The base station may receive, from the wireless device, anRAP in parallel with: one or more first TBs with a first redundancyversion (RV) associated with a HARQ process. This first transmission bythe wireless device may be based on the one or more RA parameters. Theone or more first TBs may comprise an identifier associated with thewireless device (e.g., UE ID). The base station may transmit, to thewireless device, an RAR MAC PDU comprising, e.g., a preamble identifier(e.g., RAPID), an uplink grant, a field indicating whether the one ormore first TBs are received successfully, and/or an RNTI. The RNTI maycomprise, e.g., one or more of a C-RNTI or a TC-RNTI. The uplink grantmay comprise an indication of uplink resources. The field indicatingwhether the one or more first TBs are received successfully maycomprise: one or more of the identifier associated with the wirelessdevice or a C-RNTI, if the one or more first TBs are receivedsuccessfully by the base station; or one or more of a fixed value or aTC-RNTI, if the one or more first TBs are not received successfully bythe base station. One or more transport blocks may be consideredsuccessfully received by the base station if the base station is able todecode information contained in the one or more transport blocks.Additionally or alternatively, the RAR MAC PDU may comprise at least oneMAC subheader that comprises one or more of a TC-RNTI or an indicationof a decoding failure. The base station may receive, from the wirelessdevice, one or more first TBs with a second RV associated with the HARQprocess, wherein the second RV may be the same as or different from thefirst RV. The base station may transmit, to the wireless device, adownlink packet comprising the identifier associated with the wirelessdevice, if the one or more first TBs with the first RV or the second RVare received successfully by the base station. The base station maytransmit, to the wireless device, an indication of a NACK, if TBs arenot received successfully. The base station may receive, based on theindication of the NACK, a HARQ comprising retransmitted TBs with anotherRV different from the prior first and second RVs. The base station maytransmit, to the wireless device, an indication of an ACK, if TBs aresuccessfully received. If the one or more first TBs are not receivedsuccessfully by the base station, the base station may determine thatthe RA procedure has failed and/or that a four-step RA procedure, suchas described above regarding FIG. 15 part (a), should be attempted. Thebase station may transmit, to the wireless device, an indication thatthe RA procedure has failed and/or an indication to fall back to afour-step RA procedure. A base station may perform any combination ofone or more of the above steps. A wireless device, or any other device,may perform any combination of a step, or a complementary step, of oneor more of the above steps.

Because a two-step RA procedure may reduce latency of UL data transfercompared with a four-step RA procedure, two-step RA procedures may beadvantageous for UL data transfer such as UL data arrival for a wirelessdevice in an RRC connected state or UL data arrival for a wirelessdevice in an RRC inactive state. If a wireless device is in an RRCconnected state, using two-step RA procedure may improve the latency ofreceiving an uplink grant for UL data arrival. The two-step RA proceduremay be used, e.g., if a TA timer expires or a physical-layer uplinkcontrol channel resource for the SR is not configured for a wirelessdevice. If a wireless device is in an RRC inactive state, the wirelessdevice may transmit a UL data arrival using a two-step RA procedurewithout a state transition to the RRC connected state.

If a base station configures four-step and two-step RA procedures, thebase station may use separate preamble signature groups and/or separatetime-frequency resources for each of four-step and two-step RA preambletransmissions. Using separate preamble signature groups and/or separatetime-frequency resources for different types of RA procedures may helpthe base station determine whether a wireless device attempts toinitiate a two-step RA procedure or a four-step RA procedure. A basestation may broadcast and/or unicast one or more configurationparameters that indicate separate preamble signature groups, and/or thatuse separate time-frequency resources, for four-step and two-step RApreamble transmissions.

One or more RAP groups may be configured for a two-step RA procedure viabroadcast system information. If a base station configures one or moregroups in the two-step RA procedure, a wireless device may use a size ofthe message transmitted by the wireless device in the third step, and/orthe pathloss, to determine for which group the wireless device selectsan RAP. A base station may use a group type to which an RAP belongs asan indication of the message size in the third step and/or as anindication of the radio conditions at a wireless device. A base stationmay broadcast the RAP grouping information along with one or morethresholds on system information.

A process for generating a RAP may be predetermined, or may bedetermined, e.g., using two-step RA configuration parameters. A type ofsequence for RAP generation, e.g., a Zadoff-Chu sequence, the number ofsamples in a sequence, a sub-carrier spacing for a RAP transmission, anda format of a RAP transmission in a subframe (e.g., guardtime/frequency, cyclic prefix length for a RAP transmission, and/or aresource block size allocated for an RAP and data transmission) may bepredetermined. A cell may broadcast one or more parameters, such as aroot sequence index and cyclic shift interval (e.g., rootSequenceindex,highspeedflag, and/or zeroCorrelationZoneConfig in LTE), required for awireless device to generate a set of RAPs.

The resources used for a RAP and data transmission may be pre-determinedor indicated by RA configuration parameters. A table or other form ofmemory may indicate possible pairs of system frame number (SFN) andsubframe number. A wireless device may attempt the first step of atwo-step RA procedure, e.g., transmission of an RAP and data, based onsuch a table. A base station may broadcast one or more pairs of SFN andsubframe used in the cell for the RAP and data transmission of atwo-step RA procedure. A frequency offset with which a wireless devicetransmits an RAP and data within a subframe may be configured bytwo-step RA configuration parameters. A resource via which a data partis transmitted during the UL transmission may be pre-determined orconfigured by two-step RA configuration parameters. Such a resource maybe associated with a selected RAP ID, such that a wireless devices thatselect different RAPs transmit data via different resources in the ULtransmission.

One or more wireless devices may perform the first step of a two-step RAprocedure using the same cell in the same subframe. The cell may respondto one or more wireless devices' UL transmissions by multiplexing one ormore RARs into a single MAC PDU as shown in FIG. 17. FIG. 17 is anexample MAC PDU format. Other fields may be added, e.g., to thesubheader and/or to the RARs. A MAC PDU may comprise a MAC header andMAC RARs. The MAC header may comprise one or more MAC subheaders, atleast one of which may comprise a BI. Other MAC subheaders may comprisea RAPID that may indicate an index number of one of available RAPs in acell. Each MAC RAR may comprise a wireless device ID, a C-RNTI, a TAcommand, an UL grant, and/or other parameters. A wireless device mayidentify an RAR corresponding to the wireless device in a MAC PDU byfirst identifying a subheader having a RAPID that matches the RAP thatthe wireless device transmitted during the UL transmission. The wirelessdevice may decode an RAR that is paired with the identified subheader.

The MAC PDU may comprise a subheader that may comprise a bit string,e.g., including a special bit string comprising zeros, that may bepre-defined to indicate the failure of RAP detection but success of datadecoding at a cell. The bit string may be indicated by a field of theRAPID or by a dedicated field for the bit string in the subheader. AnRAR that is a pair of the subheader having the special bit string mayinclude the wireless device ID (and/or other IDs) that a wireless devicetransmits in the UL transmission. The wireless device may decode the RARhaving a corresponding subheader that has the special bit string, todetermine whether the RAR is intended for the wireless device. The MACsubheader may comprise a field that may be a RAP identifier associatedwith the RAP if the RAP is detected. If the RAP is not detected, thefield may comprise a pre-defined format. Additionally or alternatively,a second field in the MAC PDU subheader may indicate that a RAP is notdetected.

An RAR response timer may be configured using two-step RA configurationparameters. A wireless device may reset and/or start the RAR responsetimer in response to the wireless device transmitting a UL RAP and datatransmission. The wireless device may monitor a downlink channel for anRAR on a cell until the RAR response timer is expired. A base stationmay transmit a MAC PDU that comprises one or more RARs, one or multipletimes, in a DL transmission before the RAR response timer expires. Thepresence of an RAR may be indicated via a specific channel (e.g., aPDCCH in LTE) using an identity (e.g., RA-RNTI in LTE) created based onUL transmission time (e.g., as a combination of SFN and/or subframenumber) and/or frequency offset. A wireless device may stop an RARresponse timer when at least one of the following conditions aresatisfied: the wireless device detects a MAC PDU that comprises a RAPIDmatching the RAP that the wireless device transmitted (and/or satisfyinga threshold of similarity), the wireless device determines an RAR has awireless device ID that the wireless device transmitted, and/or the RARresponse timer is expired.

A wireless device may monitor RARs for unique identifiers associatedwith the wireless device to determine whether information transmitted bythe base station is intended for the wireless device. A base station mayassign a unique identifier to each wireless device of a plurality ofwireless devices in a cell. The unique identifier may be associated witha radio network temporary identifier (RNTI). For a particular cell, theRNTI may be a cell radio network temporary identifier (C-RNTI). Awireless device may have a plurality of RNTIs associated with it, eachof which may be for a different purpose. A wireless device may monitorresources in a time and frequency resource map by identifying a C-RNTIcorresponding to the wireless device. If a base station transmitsinformation in these resources, the information may be scrambled by theunique identifier of the wireless device, e.g., C-RNTI, to which theinformation is intended. If the wireless device receives a transmissionfrom a base station, the wireless device may attempt to decode packetswith the unique identifier assigned to the wireless device by the basestation. The wireless device may determine, using its unique identifier,whether there is any data for the particular wireless device. Thewireless device may monitor one or more channels, such as downlinkcontrol channels, with its unique identifier, e.g., at least one of RNTIassigned to the wireless device, to determine whether information isintended for that particular wireless device. If the wireless deviceuses its unique identifier to attempt to decode information but is notsuccessful, then the wireless device may determine that the informationis intended for a different wireless device. The wireless device thatwas unsuccessful in its attempt to decode information may continue tomonitor the one or more channels.

A two-step RA procedure may comprise two pairs of transmission, e.g., afirst pair for a preamble transmission and a second pair for datatransmission. Four overall outcomes may be possible from these pairs oftransmission: both pairs succeed, both pairs fail, the first pairsucceeds but the second pair fails, or the second pair succeeds but thefirst pair fails. A wireless device may determine, based on anindication in a MAC subheader such as described above, whether one ormore preamble transmissions are successfully received by a base station.A wireless may determine, based on an indication in a MAC RAR such asdescribed above, whether one or more data transmissions are successfullyreceived by a base station. If either one or more preamble transmissionsare not successfully received by a base station, and/or if either one ormore data transmissions are not successfully received by a base station,a wireless device may determine whether to perform a retransmission ofat least one of the first pair and/or the second pair of transmissions.If a wireless device determines to perform a retransmission, thewireless device may determine when to perform the retransmission.

A contention resolution may be completed based on, e.g., either a C-RNTIor a wireless device contention resolution identity in an RAR. If a basestation detects an RAP and decodes one or more TBs or portion thereofthat a wireless device transmits, the base station may respond with anRAR that comprises the C-RNTI and/or other wireless device identifiersthat the wireless device transmits in the first step of a two-step RAprocedure. By detecting the C-RNTI and/or other wireless deviceidentifiers in the received RAR, the wireless device may determine thesuccess of the two-step RA procedure. The wireless device may startmonitoring the downlink control channel associated with the C-RNTI (orTemporary C-RNTI) from the time the wireless device detects the C-RNTI(or Temporary C-RNTI) in the RAR such as shown in FIG. 21.

If a base station detects an RAP but fails to decode one or more TBs orportion thereof that a wireless device transmits in the UL transmissionof the two-step RA procedure, the base station may indicate such afailure. The base may transmit a MAC PDU that comprises a TC-RNTI,and/or one or more indicators in a MAC subheader and/or in an RAR, thatmay indicate a decoding failure to the wireless device of the RAP thatthe base station detected but failed to decode. A wireless device maydetermine, based on the one or more indicators, that the RAP was notsuccessfully received or decoded by the base station. The wirelessdevice may re-transmit the one or more transport blocks, e.g., byperforming HARQ retransmission. The wireless device may start amac-ContentionResolution Timer when the wireless device retransmits,based on uplink grant in the RAR, the one or more transport blocks. Thewireless device may not start a mac-ContentionResolution Timer when thewireless device transmits one or more transport blocks based on uplinkgrant in the RAR, if the RAR indicates that one or more transport blocksare received and decoded successfully by the base station.

A wireless device may restart the mac-ContentionResolutionTimer at aHARQ retransmission. If a wireless device starts or restarts themac-ContentionResolutionTimer, the wireless device may start monitoringa downlink control channel using the C-RNTI or TC-RNTI. The wirelessdevice may start this monitoring at a subframe and/or at a time offsetfrom a start or restart of the mac-ContentionResolutionTimer. If an RARindicates that one or more transport blocks are received successfully bya base station, the wireless device may monitor the C-RNTI and/orTC-RNTI. The wireless device may start this monitoring at a subframeand/or at a time offset from receiving the RAR.

If a wireless device transmits a C-RNTI in the first step of a two-stepRA procedure, the wireless device may monitor a downlink control channelusing the C-RNTI. If a wireless device does not transmit a C-RNTI in thefirst step of a two-step RA procedure, the wireless device may monitor adownlink control channel using the TC-RNTI. If themac-ContentionResolutionTimer expires, a wireless device may determinethat the two-step RA procedure has failed.

FIG. 21 shows an example of contention resolution for a two-step RAprocedure. At step 2101, a wireless device may transmit, to a basestation and via a cell, a random access preamble (RAP) and data. Thebase station associated with the cell may receive the RAP and the data.The RAP may include an identifier (e.g., RAPID=xxx). The data maycomprise UL data and a redundancy version (e.g., RV=aa). The data maycomprise an identifier of the wireless device (e.g., UE ID=yyy). Thewireless device may start an RAR response timer (e.g.,mac-ContentionResolutionTimer) at or near the time the wireless devicetransmits the RAP and data. At step 2102, the base station may transmit,and the wireless device may receive, a MAC PDU comprising a subheaderthat includes a RAP identifier of the RAP (e.g., RAPID=xxx). The MAC PDUmay also comprise an RAR that may correspond to the subheader comprisingan uplink grant. The RAR may include one or more indications of adecoding failure by the base station of the UL data. If an indication ofa decoding failure is turned off, the wireless device may startmonitoring a downlink control channel with a C-RNTI of the wirelessdevice. At step 2103, if an indication of a decoding failure is turnedon, the wireless device may perform a HARQ retransmission of the RAP anddata, the wireless device may start monitoring the downlink controlchannel with the C-RNTI of the wireless device, and/or the wirelessdevice may start and/or restart a timer (e.g., themac-ContentionResolutionTimer).

The wireless device may transmit one or more transport blocks in a firstsubframe and via radio resources indicated in an uplink grant. Thewireless device may start a contention resolution timer in the firstsubframe depending on whether the RAR comprises the identifier of thewireless device. The wireless device may stop monitoring for RAR(s),e.g., after decoding a MAC packet data unit for an RAR and determiningthat the RAP identifier matches the RAP transmitted by the wirelessdevice. The MAC PDU may comprise one or more MAC RARs and a MAC header.The MAC header may comprise a subheader having a backoff indicator andone or more subheaders that comprises RAPIDs.

If one or more data transmissions are successfully received by a basestation, the base station may transmit a MAC PDU comprising one or morecorresponding RARs that each comprise an uplink grant. The uplink grantmay indicate a particular subframe for a wireless device to transmituplink data. The wireless device may start monitoring a downlink controlchannel from a second subframe. The wireless device may determine thesecond subframe based on, e.g.: a third subframe in which an RAR isreceived, if the RAR comprises the wireless device identifier; and/orthe first subframe in which the wireless device transmits uplinkresources based on the uplink grant. The wireless device may monitor thedata for a C-RNTI, if the data comprises a C-RNTI; and/or the wirelessdevice may monitor the RAR for a Temporary C-RNTI (TC-RNTI), if the datadoes not comprise a C-RNTI.

If a wireless device does not receive any MAC PDU that comprises theRAPID and/or the wireless device identifier associated with the RAP, andif an RAR response timer has expired, the wireless device may retry thefirst step of a two-step RA procedure. The wireless device mayretransmit the RAP and the data on the same cell.

If the wireless device receives a MAC PDU that comprises a BI, thewireless device may select a backoff time. The backoff time may berandom, and it may be determined according to a uniform distribution,e.g., between 0 and a BI value. The wireless device may delay thesubsequent re-transmission of the RAP and the data by the selectedbackoff time. If the wireless device receives a MAC PDU that does notcomprise any backoff indicator until an RAR response timer has expired,the backoff time may be set to zero. The wireless device may have acounter for counting the number of retransmissions of RAP and data. Thewireless device may set the counter to zero (or 1) in the initial RAPtransmission, and the wireless device may increase the counter by onewhenever the wireless device re-tries the first step of a two-step RAprocedure. The wireless device may reset the counter to zero (or 1) whenthe wireless device receives any MAC PDU that comprises the RAP ID orthe wireless device ID, and/or when an RAR response timer expires.Two-step RA configuration parameters may have a parameter limiting anallowed maximum number of the retransmissions of RAP and data. If thecounter reaches the maximum number, the wireless device may stopretransmission. The wireless device may perform a new RA on another cellwith two-step or four-step RA procedure depending on two-step RAconfiguration parameters of a cell associated with the another cell.

FIG. 22 shows an example of a two-step RA procedure and the failure ofUL transmission for n times. At step 2201, a first base station (e.g.,base station A) may transmit, via a first cell (e.g., cell A_a),two-step RA configuration parameters to a wireless device. The wirelessdevice may determine a RAP selection, at step 2202, e.g., comprising oneor more RAP selections procedures described herein. At step 2203, thewireless device may transmit a RAP and data (e.g. one or more transportblocks) of a two-step RA procedure to a base station. The RAP maycomprise an identifier (RAP ID=xxx), and the data may comprise awireless device identifier (UE ID=yyy). At or near the time the wirelessdevice transmits the RAP and the data, the wireless device may start anRAR response timer. The base station may successfully decode andidentify a RAP ID associated with the RAP, but the base station may failto decode the data. Failure to decode the data may result from, e.g.,collision or low signal quality. The base station may not transmit anRAR to the wireless in response to the RAP and data, or the base stationmay transmit an RAR comprising an indication of a decoding failure ofthe data. If the RAR response timer expires, and if the wireless devicehas not received an RAR indicating that the RAP and the data weresuccessfully received by the base station, at step 2204, the wirelessdevice may retransmit the RAP and the data after a time periodcorresponding to a backoff time. The wireless device may perform theabove steps 2203 through 2204, to retransmit the RAP and the data, nnumber of times, where n may be any whole number. After the nthretransmission at step 2205, and after the RAR response timer expireswith the wireless device not receiving an RAR indicating that the RAPand the data were successfully received by the base station, thewireless device may receive RA configuration parameters from a secondbase station (e.g., base station B) via a second cell (e.g., cell B_a),at step 2206. The RA configuration parameters from the second basestation may be for a two-step RA procedure or for a four-step RAprocedure. At step 2207, the wireless device may determine, based on theRA configuration parameters from the second base station, a RAPselection, e.g., comprising one or more RAP selections proceduresdescribed herein. The wireless device may transmit, to the second basestation, a new RAP (e.g., comprising RAP ID=zzz) and the data (e.g.,comprising the UE ID=yyy). The wireless device may repeat any of theabove steps until the wireless device determines that a RA procedure issuccessful.

The wireless device may receive a MAC PDU comprising a subheader thatincludes a RAP ID that the wireless device transmitted, but that alsoincludes a decoding failure indicator in the subheader or in the RARassociated with the subheader. The decoding failure indicator may beimplemented in different ways depending on a MAC PDU format. If RARs fordata decoding failures and successes have the same size, a MAC PDU mayhave a dedicated field inserted in a subheader or in an RAR to indicatethe data decoding success or failure. This field may comprise one bit,such that either zero or one may indicate data decoding success orfailure. A special bit string may be also used in an existing field inan RAR to indicate data decoding success or failure. This special bitstring may comprise, e.g., all zeros or a detectable pattern of ones andzeros in the field of a wireless device ID in an RAR to indicate datadecoding failure, or to indicate data decoding success. If RARs for datadecoding failure and success have the same size, a wireless device maydetermine, based on a pre-determined RAR size information, the boundaryof an RAR in a MAC PDU. If RARs for data decoding failure and successhave different sizes, the base station may insert a field, to indicateRAR size information, in a MAC subheader or in an RAR. A wireless devicemay determine the boundary of an RAR in a MAC PDU based on the field. IfRARs for data decoding failure and successes have different sizes, theRARs may have different formats. For example, an RAR for a data decodingfailure may comprise a field of Temporary Cell Radio Network TemporaryIdentity instead of a field of a contention resolution wireless deviceID, and an RAR for a data decoding success may comprise a contentionresolution wireless device ID instead of a TC-RNTI.

A wireless device may transmit, to a base station and as a part of atwo-step RA process, a random access preamble and one or more transportblocks. The wireless device may receive a MAC PDU comprising: one ormore MAC PDU subheaders, wherein a subheader comprises an RAPidentifier; and one or more RARs, wherein each RAR corresponds to a MACPDU subheader in the one or more MAC PDU sub-headers. The wirelessdevice may determine whether the one or more transport blocks arereceived successfully based on one or more of: a first field in thesubheader (e.g., a bit in the subheader indicating a fall back to afour-step RA procedure); a second field in an RAR associated with afirst sub-header comprising an RAR identifier associated with the RAR(e.g., a bit in the RAR indicating a fall back to a four-step RAprocedure). The wireless device may retransmit one or more transportblocks, if the one or more transport blocks are not receivedsuccessfully by a base station. The wireless device may determine a sizeof the RAR based on one or more indications in the first field and/or inthe second field. The wireless device may determine whether to fall backto a four-step RA procedure based on one or more indications in thefirst field and/or in the second field.

A wireless device may perform a method for determining whether atwo-step RA procedure has failed based on one or more timers. A wirelessdevice may receive, from a base station, RA configuration parameters.The wireless device may transmit, to a base station, an RAP and one ormore first transport blocks. The one or more first transport blocks maycomprise an identifier of the wireless device (e.g., UE ID). Thewireless device may receive, from the base station, a MAC PDU comprisingone or more MAC subheaders and one or more RARs. At least one of the oneor more MAC subheaders may comprise a RAPID of the RAP transmitted bythe wireless device. Each RAR of the one or more RARs may be associatedwith a MAC subheader of the one or more MAC subheaders. A first RAR maybe associated with a first MAC header comprising an uplink grant for afirst subframe. The wireless device may transmit, to the base station,in a first subframe, and via radio resources indicated by the uplinkgrant, one or more transport blocks. The wireless device may start, inresponse to transmitting one or more transport blocks, and based onwhether the RAR comprises the identifier of the wireless device, acontention resolution timer. The contention resolution timer may be fordetermining whether a random access procedure is successful. Thewireless device may stop, based on a determination that the RAPID of theMAC subheader matches the identifier of the wireless device, an RARresponse timer that started in response to transmitting the RAP. Thewireless device may stop, based on a determination that a downlinkcontrol information detected from a downlink control channel comprisesthe identifier of the wireless device, the contention resolution timer.The wireless device may perform one or more operations regarding thecontention timer one or more times, and/or using one or more timers. Thewireless device may restart, based on a retransmission of the one ormore TBs, the contention resolution timer. The wireless device maydetermine that, based on an expiration of the contention resolutiontimer, a first RA procedure has failed. The wireless device mayinitiate, at a time period after determining that the first RA procedurehas failed, a second RA procedure. The wireless device may determine,based on a backoff indicator in the RAR, the time period. The wirelessdevice may monitor a downlink control channel associated with an RNTI.The wireless device may start the monitoring from a second subframe. Themonitoring by the wireless device may comprise monitoring the downlinkcontrol channel for a downlink control information associated with theRNTI. The wireless device may determine the second subframe based on oneor more of: a subframe in which an additional RAR is received thatcomprises the identifier of the wireless device; and/or a subframe inwhich the wireless device transmits uplink resources based on the uplinkgrant. The monitoring may be performed after detecting the RARcomprising the RNTI. The RNTI may comprise one or more of a C-RNTI or aTC-RNTI. The wireless device may determine that an RAR associated withthe RAP has not been received. The wireless device may perform thefollowing one or more times: retransmitting the RAP and the one or moretransport blocks; starting, based on the retransmitting the RAP and theone or more transport blocks, a second timer; and determining that anRAR associated with the retransmitted RAP has not been received. Thisdetermining may occur at a second time period after the starting of thesecond timer. The wireless device may determine, based on adetermination that an RAR associated with one or more retransmissions ofthe RAP has not been received, that an RA procedure with the basestation has failed. The wireless device may receive, from a second basestation, RA parameters. The wireless device may transmit, to the secondbase station, the RAP and the one or more transport blocks. A wirelessdevice may perform any combination of one or more of the above steps. Abase station, or any other device, may perform any combination of astep, or a complementary step, of one or more of the above steps.

A base station may multiplex, in a MAC PDU, RARs for two-step andfour-step RA procedures. If RARs for two-step and four-step RA procedurehave the same size, a wireless device may not require an RAR lengthindicator field and/or the wireless device may determine the boundary ofeach RAR in the MAC PDU based on pre-determined RAR size information.The RAR may have a field to indicate a type of RAR (e.g., comprising oneor bits in a reserved “R” field as shown in FIG. 23). An RAR maycomprise different formats for two-step and four-step RARs with a fixedsize. Some examples for different RAR formats are shown in FIG. 23 parts(a), (b), and (c). By using RARs with different formats, the size of thesub-header may be reduced and/or additional bits may be available forother fields. Encoding RARs with an indication of an RAR type may reducedownlink signaling overhead.

FIG. 24 shows an example RAR format that may or may not comprise a fieldto indicate a type of RAR. The RAR shown in FIG. 24 may comprise a fixedsize using the same format for two-step and four-step RA. If RARs fortwo-step and four-step RA procedures have different sizes, a field forindicating an RAR type may be included in a subheader (such as a MACsubheader) or in an RAR. An RAR may comprise different types of fieldsthat may correspond with an indicator in a subheader or in an RAR. Awireless device may determine the boundary of one or more RARs in a MACPDU based on one or more indicators.

Different message formats may be used based on the type of device forcommunication. If a wireless device comprises, e.g., an IoT device, suchas a smart appliance or other electronics equipment that may not requirea large amount of data transmission, the format may include a smallmessage space for transmissions by the device instead of including anuplink grant. If the wireless device comprises, e.g., a phone, tablet,or other device that requires a large amount of data transmissions, theformat may include an uplink grant for larger transmissions.

A wireless device may determine whether an RAR is a two-step RAR or afour-step RAR, at least based on the RAP identifier in the correspondingMAC PDU sub-header. Two-step and four-step RA preamble identifiers maybe selected from two different preamble groups. The wireless device maydetermine whether an RAR is a two-step RAR or a four-step RAR, at leastbased on a field indicating an RAR type. The MAC PDU subheader maycomprise the field indicating an RAR type. The field may comprise onebit indicating a two-step or a four-step RAR type. The RAR length may bepredetermined for each RAR type. A wireless device may determine a sizeof an RAR based on a determination of whether the RAR is a two-step RARor a four-step RAR.

A wireless device may transmit, to a base station, a random accesspreamble via a random access channel in a subframe and using a frequencyoffset. A wireless device may determine an RA-RNTI based on one or moreof a subframe number and/or a frequency index. A wireless device maymonitor a control channel for a control packet associated with anRA-RNTI. A wireless device may receive a MAC PDU, associated withRA-RNTI, comprising: one or more MAC PDU subheaders, wherein a subheadermay comprise an RAP identifier; one or more RARs, wherein each RAR ofthe one or more RARs may correspond to a MAC PDU subheader of the one ormore MAC PDU sub-headers; and an uplink grant. The wireless device maytransmit one or more transport blocks based on the uplink grant.

Example RAR formats are shown in FIGS. 19, 23, and 24. An RAR mayinclude one or more fields, such as a timing advance command, an uplinkgrant, a TC-RNTI, a C-RNTI, a wireless device (e.g., a UE) contentionresolution identity, and/or other parameters. An RAR format may bedetermined based on the fields that are needed in the RAR. A present bitmay be used for a field to indicate whether the field is included in theRAR. For example, a presence field may indicate whether or not an RARincludes an uplink grant. Other fields may be associated with a presencefield. Multiple RAR types may include different fields that may bepre-defined. A field in the MAC subheader or in an RAR may determine theRAR type and a corresponding RAR length. A two bit field may indicatewhich of four or three RAR types are transmitted. Other fields,comprising any number of its, may be included in the MAC subheaderand/or in an RAR to indicate information about an RA procedure.

FIG. 19 shows example RAR formats with a fixed size (e.g., 6 bytes) forvarious RA procedures (e.g., two-step and four-step RA procedures). FIG.23 parts (c) and (a) show example RAR formats with a fixed size (e.g., 6bytes) for two-step and four-step RA procedures, respectively. FIG. 23part (b) shows an example RAR format with a fixed size (e.g., 8 bytes)for a two-step RA procedure. FIG. 24 shows an example RAR format with afixed size (e.g., 12 bytes) for two-step and four-step RA procedures. Asshown in FIGS. 23 parts (a)-(c) and FIG. 24, an RAR format may comprise,e.g., one or more: reserved fields (e.g., “R”), timing advance command,uplink grant, temporary C-RNTI (TC-RNTI), and/or wireless device (e.g.,UE) contention resolution identity.

A two-step RA procedure may comprise a hybrid automatic repeat request(HARQ), including, e.g., HARQ with soft combining, if a data decodingfailure occurs. If a wireless device receives a MAC PDU that comprises asubheader with a RAP ID that matches or indicates the RAP that wastransmitted by the wireless device, but a decoding failure indicatorindicates a failure has occurred, the wireless device may perform HARQ.The wireless device may perform HARQ, e.g., by transmitting anotherredundancy version to the cell from which the wireless device receivedthe MAC PDU. The HARQ transmission may occur at an a priori knownsubframe or time period, such as every eight subframes, after a priorHARQ transmission in the same HARQ process. The HARQ may predetermine asequence of redundancy version numbers that the wireless device maytransmit in a HARQ transmission in the same process. An RV number maystart, e.g., from zero or one in an initial UL data transmission, andthe next RV in the sequence may be transmitted if a wireless devicedetermines that an RAR comprises an indicator requesting a next RV.

FIG. 25 shows an example of an RA procedure using HARQ retransmission. AHARQ retransmission may occur if a wireless device detects a RAPID in acell but determines that the base station failed to decode datatransmitted by the wireless device. At step 2501, a wireless device mayreceive, from a base station and via a cell, RA configurationparameters. At step 2502, the wireless device may determine an RAPselection, e.g., comprising one or more RAP selections proceduresdescribed herein. At step 2503, the wireless device may transmit an RAP(e.g., comprising an RAP ID=xxx) and UL data (e.g., comprising a firstRV=aa, and UE ID=yyy). At or near step 2503, the wireless device maystart or restart an RAR response timer. At step 2504, the base stationmay transmit, and the wireless device may receive, a MAC PDU comprisinga subheader (e.g., comprising RAP ID=xxx), such as a MAC subheader, witha TC-RNTI and a decoding failure indicator. Based on receiving thedecoding failure indicator, the wireless device may stop the RARresponse timer. At step 2505, the wireless device may transmit a HARQretransmission of the RAP and the UL data. The HARQ retransmission maycomprise a second RV (e.g., RV=bb). The wireless device may transmit theHARQ retransmission based on a determination that a decoding failure hasoccurred (e.g., which may be indicated by the decoding failureindicator). At or near step 2505, the wireless device may start acontention resolution timer. At step 2506, the base station maytransmit, to the wireless device, a NACK. The base station may transmitthe NACK transmission based on receiving the HARQ retransmission. Basedon receiving the NACK, the wireless device may stop the contentionresolution timer. At step 2507, the wireless device may transmit asecond HARQ retransmission of the RAP and the UL data. The second HARQretransmission may comprise a third RV (e.g., RV=cc). The wirelessdevice may transmit the second HARQ retransmission based on the wirelessdevice receiving the NACK. At or near step 2507, the wireless device maystart or restart a contention resolution timer. At step 2508, the basestation may transmit, to the wireless device, an ACK. The wirelessdevice may receive the ACK. Based on receiving the ACK, the wirelessdevice may determine that the second HARQ retransmission was successful.Based on receiving the ACK, the wireless device may stop the contentionresolution timer.

For RA procedures using HARQ retransmission, each RV may be transmittedin an adaptive or in a non-adaptive manner A base station may transmit,to a wireless device and via a cell, one or more indicators of a HARQtransmission type. For example, the base station may transmit, to thewireless device and via a downlink control channel, a new data indicator(NDI) with downlink control information (DCI). Additionally oralternatively, the base station may transmit, to the wireless device andvia a downlink HARQ indicator channel, a one-bit HARQ acknowledgement(ACK) or non-acknowledgement (NACK). The wireless device may determine,based on the ACK or NACK, whether to transmit, to the base station andvia the cell, another RV. If the wireless device detects an NDI thatdiffers from a previously received NDI (e.g., an NDI bit has changed),the wireless device may, regardless of a HARQ ACK or NACK, transmitanother RV specified in the DCI. The wireless device may transmit thisRV using a resource and modulation and coding scheme (MCS) specified inthe same DCI. If the wireless device detects a NDI non-toggled butreceives a HARQ NACK message, the wireless device may transmit apredefined RV with the same resource and MCS as the previous HARQtransmission.

The maximum number of HARQ transmissions may be determined for atwo-step RA procedure, e.g., by maxHARQ-Msg3Tx in LTE. A wireless devicemay have a counter for counting the number of HARQ transmissions. Awireless device may set the counter to one based on transmitting thefirst RV. The wireless device may increase the counter by one based ontransmitting a next RV in the cell. If the counter reaches the maximumnumber of HARQ transmissions configured in a cell (or a retransmissionthreshold and/or a HARQ transmission threshold), a wireless device maydetermine that the two-step RA procedure has failed. If the wirelessdetermines that the two-step RA procedure has failed, the wirelessdevice may perform a new RA procedure on a different cell, the same RAprocedure but on a different cell, or a new RA procedure on the samecell. The new RA procedure may comprise a two-step or a four-step RAprocedure.

FIG. 26 shows an example of a two-step RA procedure failure as thenumber of HARQ retransmission reaches a threshold. Each of FIG. 26 steps2601 through 2607 correspond to FIG. 25 steps 2501 through 2607,respectively, the descriptions of which are incorporated by referencehere for FIG. 26 steps 2601 through 2607. At step 2608, the base stationmay transmit, and the wireless device may receive, a second NACK. Steps2607 and 2608 may be repeated any number of times, wherein each HARQretransmission may include a different RV, up to a final HARQretransmission and NACK at steps 2609 and 2610, respectively. The finalHARQ retransmission may be based on the total number of HARQretransmissions reaching a threshold value, such as indicated bymaxHARQ-Msg3Tx. At step 2611, if the threshold value for HARQretransmissions is reached, and if a wireless device receives a NACK(e.g., at step 2610) and/or the contention resolution timer expireswithout the wireless device receiving an ACK, then the wireless devicemay determine that the RA procedure has failed. A base station maydetermine that an RA procedure has failed, e.g., if the base station isunsuccessful in decoding a threshold number of HARQ retransmissions,and/or if the base station does not receive a HARQ retransmission fromthe wireless device after a threshold period of time.

A wireless device may determine that a two-step RA procedure issuccessful, e.g., if, prior to the expiration of an RAR response timer,the wireless device receives a MAC PDU that comprises the same RAP IDand wireless device ID that a wireless device transmitted in the ULtransmission. An RA procedure may be successful if a base stationidentifies the wireless device's transmitted RAP, decodes the wirelessdevice's transmitted data, and transmits, to the wireless device andbefore the wireless device's RAR timer expires, a MAC PDU comprising theRAP ID and wireless device ID. A base station may identify an RAP IDbased on a peak detector. The peak detector may detect a peak fromcorrelation outputs between a received signal and a set of RAPsavailable to a cell. If the resource block, over which the data orportion thereof is transmitted during the UL transmission, is associatedwith an RAP, an RAP ID may also be detectable based on an energydetector. The energy detector may measure an energy level of theresource block for a UL data transmission.

FIG. 27 shows an example of a successful two-step RA procedure, e.g.,wherein a base station decodes an RAP and UL data, and a base stationresponds by transmitting an RAR to a wireless device. Each of FIG. 27steps 2701 through 2703 correspond to FIG. 20 steps 2001 through 2003,respectively, the descriptions of which are incorporated by referencehere for FIG. 27 steps 2701 through 2703. At or near step 2703, thewireless device may start or restart an RAR response timer. At step2704, the base station may transmit, to the wireless device, a MAC PDUcomprising one or more MAC subheaders and one of more RARs. At least oneof the MAC subheaders in the MAC PDU may comprise a RAP ID (e.g., RAPID=xxx) that may correspond to the RAP ID included in the RAP that wastransmitted by the wireless device in step 2703. At least one of theRARs in the MAC PDU may comprise an identifier associated with thewireless device (e.g., UE ID=yyy) that may correspond to the identifiertransmitted by the wireless device in step 2703. If the wireless devicedetermines that the RAP ID included in at least one of the MACsubheaders corresponds to the wireless device's RAP IP; if the wirelessdevice determines that an RAP, corresponding to the MAC subheader withthe wireless device's RAP ID, comprises the wireless device'sidentifier; and if the RAR response time has not expired; then thewireless device may determine that the two-step RA procedure wassuccessful.

A wireless device may transmit in parallel, to a base station and via afirst cell, a random access preamble, and one or more transport blockswith a first RV associated with a HARQ process, wherein the one or moreTBs comprise the wireless device ID. The wireless device may receive anRAR MAC PDU comprising one or more of: a preamble identifier; an uplinkgrant; a field indicating whether the one or more TBs are receivedsuccessfully; and/or an RNTI. The wireless device may transmit, usinguplink resources, the one or more TBs with a second RV different fromthe first RV associated with the HARQ process. The uplink resources maybe identified in the uplink grant. The wireless device may receive adownlink packet comprising the wireless device ID, if the one or moreTBs are decoded successfully. The wireless device may receive one ormore messages comprising configuration parameters of a RACH of a firstcell.

A wireless device may handover from a source base station to a targetbase station. A handover may occur, e.g., if the wireless device movesfrom a location in a first cell served by the source base station to alocation in a second cell served by the target base station, if thesource base station is unable to accommodate communications with thewireless device, if it is determined that a different base station is abetter candidate for accommodating communications with the wirelessdevice than the source base station, or for various other reasons.

A random access procedure may be optimized for a handover of a wirelessdevice from a source base station to a target base station. Suchoptimization may provide a faster handover, with reduced latency, andmay provide a handover without suffering from collisions with othertransmissions. A wireless device may perform, with a target basestation, a contention-based four-step random access procedure that maytake, e.g., 20 ms, a contention-free three-step random access procedurethat may take, e.g., 14 ms, and/or a contention-based two-step randomaccess procedure that may take, e.g., 4 ms. By communicating randomaccess information from a target base station to a wireless device(e.g., via a source base station), prior to performing random access,the wireless device may employ a contention-free two-step random accessprocedure that may take, e.g., 1 ms. A contention-free, two-step randomaccess procedure for handover with the above advantages may be achievedby communicating random access information with handover messagingdescribed below.

A source base station and a target base station for a possible handovermay perform different operations for RA procedures to initiatecommunications with the wireless device. Additionally or alternatively,a wireless device that is a candidate for a handover may be capable orincapable of one or more types of RA procedures, and/or conditions in acell of the source base station may differ from conditions in a cell ofa target base station. For one or more reasons, prior to initiating ahandover of a wireless device from a source base station (e.g., an eNB,a gNB, etc.) to a target base station (e.g., an eNB, a gNB, etc.), adevice may determine a type of random access procedure to use to performthe handover. The type of RA procedure may include, e.g., a two-step RAprocedure or a 4-step RA procedure. Additionally or alternative, thetype of RA procedure may include, e.g., whether the RA procedure iscontention-based (such as a contention-based four-step RA proceduredescribed above regarding FIG. 15 part (a)) or contention-free (such asa three-step contention-free RA procedure described above regarding FIG.15 part (b), or a two-step contention-free RA procedure available thatmay be used for handover). The device that may determine the type of theRA procedure may be a target base station, a source base station, and/ora core network device (e.g., located at a Next Generation Core (NGC)network entity). Additionally or alternatively, a wireless device maydetermine the type of the RA procedure, e.g., based on random accessinformation received in one or more messages. As an example, a sourcebase station may send to a target base station information about thetype of RA procedure (e.g., a contention-free two-step RA procedure) toperform for a wireless device that may be a candidate for a handoverfrom the source base station to a target base station. Information aboutthe type of RA procedure may also be sent by the target base station tothe source base station, and by the source base station to the wirelessdevice.

A wireless device may receive random access information from a sourcebase station for accessing a target cell. The random access informationmay comprise, e.g., an indication of a type of random access procedure,such as a two-step random access procedure or a four-step random accessprocedure, for the wireless device. The random access information mayalso comprise timing advance information for uplink transmissions and/ordownlink transmissions for the wireless device in the target cell, suchas for a random access preamble, a random access response, and/or one ormore transport blocks. The timing advance information may indicate,e.g., whether the timing advance value is zero or not, and/or anestimated time advance value. Receiving the random access informationfrom a source base station, as opposed to waiting to receive systeminformation comprising random access information for a target basestation, may enable a wireless device to reduce handover delay. Thewireless device may perform a random access procedure as part of ahandover to a target cell based on one or more elements of receivedrandom access information.

FIG. 28 shows an example of a random access procedure for handover, suchas via a direct interface. At step 2810, a wireless device 2801 (e.g., aUE, or any device capable of communicating with a network) may send, toa source base station 2802 (e.g., a source gNB), a first messagecomprising a measurement report for one or more cells. The measurementreport may be based on one or more attributes of the one or more cells.The measurement report may comprise, e.g., at least one of a list ofcells, an RSRP (Reference Signal Received Power) for a cell or for eachof a plurality of cells included in a list of cells, an RSRQ (ReferenceSignal Received Quality) for a cell or for each of a plurality of cellsin a list of cells, cell priority of one or more base stations includinga cell priority of the target base station 2803, or other informationthat may be used in a handover decision. The wireless device 2801 maygenerate the measurement report from measurements of neighboring cells,and the measurement report may indicate one or more base stations, of aplurality of neighboring base station, that may be candidates for ahandover of the wireless device 2801 from the source base station 2802based on power measurements for each base station. The wireless device2801 may generate the measurement report using the procedures describedbelow regarding FIG. 30.

The source base station 2802 may determine a handover decision at step2820. The handover decision may be based on the measurement report. Thesource base station 2802 may determine a target base station 2803, fromamong a plurality of potential target base stations. The source basestation 2802 may determine, based on one or more elements of themeasurement report, whether or not to initiate a handover procedure forthe wireless device 2801. If the base station 2802 determines that ahandover should be performed, the base station 2802 may send a secondmessage, at step 2830, to a target base station 2803 (e.g., a targetgNB). The second message may comprise a handover request message. Thesecond message may also comprise one or more of the measurement reportfrom the first message, an identifier of the wireless device 2801, awireless device context (e.g., one or more bearers, one or more slices,subscriber information, security information, etc.), capabilityinformation of the wireless device 2801 (e.g., one or more types of RAprocedures the wireless device 2801 is capable of performing), one ormore cell identifiers of a cell or of a plurality of cells served by thetarget base station 2803, one or more elements of the measurement reportreceived from the wireless device 2801, or other information that may beused for performing a handover. The source base station 2802 may performthe handover decision in step 2820, and the source base station 2802 mayreceive and send the first and second messages in steps 2810 and 2830,respectively, using the procedures described below regarding FIG. 31.

The target base station 2803 may receive the second message, at step2830. The target base station 2803 may process the handover request. Thetarget base station 2803 may determine, based on the second message,whether or not to accept the handover request for the wireless device2801. The target base station 2803 may provide an acknowledgement of thehandover request, e.g., by sending, at step 2840, a third message to thesource base station 2802. The target base station 2803 may process thehandover request, and the target base station 2803 may receive and sendthe second and third messages in steps 2830 and 2840, respectively,using the procedures described below regarding FIG. 32.

The third message, that may be sent by the target base station 2803 tothe source base station 2802, may comprise a handover requestacknowledgement and random access information, including, e.g., anindication of a type of a random access procedure. The handover requestacknowledgement may comprise an ACK that may be in response to thehandover request. The target base station 2803 may determine randomaccess information for inclusion in the handover requestacknowledgement. The target base station 2803 may send the third messagebased on determining to accept the handover request. The target basestation 2803 may include in the third message a handover requestacknowledge message as well as random access information.

In a handover procedure, the handover related information may betransmitted by an upper layer message, such as an RRC message. A type ofa random access procedure, such as a two-step random access procedure ora four-step random access procedure, may be indicated, e.g., by one ormore RACH type indication parameters in an RRC connectionreconfiguration message. The RRC reconfiguration message may be includedwith a handover command Additionally or alternatively, one or more RACHtype indication parameters may comprise one or more indications of acapability (e.g., configured for a contention-free two-step RAprocedure) or an incapability (e.g., not configured for acontention-free two-step RA procedure). With respect to one or moreindications of incapability, one or more default RA procedures may beindicated in the random access information of the third message (e.g.,instructing a wireless device to default to a contention-based four-stepRA procedure). Mobility control information (e.g., mobilityControlInfo)in an RRC connection reconfiguration message (e.g.,RRCConnectionReconfiguration) may comprise one or more of the RACH typeindication parameters. A target NG-RAN node to a source NG-RAN nodetransparent container may comprise RRC parameters comprising a handovercommand and/or one or more of the RACH type indication parameters. Thehandover command may comprise, e.g., an RRC E-UTRA handover commandmessage, such as handoverCommandMessage. Additionally or alternatively,a type of a random access procedure may be indicated by one or moreparameters in a mobility control information. The mobility controlinformation may further indicate one or more of: mobilityControlInfoV2X,handoverWithoutWT-Change, makeBeforeBreak, rach-Skip, orsameSFN-Indication.

The random access information may comprise, e.g., at least one of afirst indication indicating that a random access procedure for handoverexecution should be performed with one of a two-step random accessprocedure or a four-step random access procedure, a second indicationfor performing a two-step random access process, a preamble identifierfor a two-step random access procedure, and/or a preamble identifier fora four-step random access procedure. The preamble identifier for atwo-step random access procedure and/or a four-step random accessprocedure may be used to determine radio resources, e.g., for channelaccess by the wireless device 2801. The preamble identifier may compriseone or more of a preamble index, PRACH mask index, root sequence, and/orthe preamble, each of which may be used by the wireless device 2801 fora random access procedure. The random access information may furthercomprise a random access channel configuration information for atwo-step random access procedure and/or radio resource configurationparameters for a two-step random access procedure. Additionally oralternatively, the third message may comprise, e.g., one or more of: ahandover request acknowledgment, one or more bearers admitted, one ormore slices admitted, one or more cells served by the target basestation 2803, radio resource configuration information (e.g., RACHconfiguration, channel configuration information, etc.) for the wirelessdevice 2801, one or more types of random access procedures, and/ormobility control information for the wireless device 2801. The thirdmessage may further comprise timing advance information, e.g., fortransmission of uplink data. The timing advance information may compriseat least one of an indication of a zero timing advance and/or a firstvalue for the timing advance. The first value for the timing advance maybe estimated by, e.g., the source base station 2802, the second basestation 2803, and/or another device, such as a core network devicedescribed further below regarding FIG. 29.

The second message and/or the third message may be exchanged directly,e.g., via a direct interface such as an Xn interface, between the sourcebase station 2802 and the target base station 2803. Additionally oralternatively, one or more elements of the second message and/or one ormore elements of the third message may be exchanged indirectly, e.g.,via one or more core network entities.

At step, 2840, the source base station 2802 may receive the thirdmessage. The source base station 2802 may send, to the wireless device2801 and based on the third message, a fourth message, at step 2850. Thefourth message may comprise, e.g., a handover command and random accessinformation. The handover command may comprise a command for thewireless device 2801 to execute a handover towards a cell of the targetbase station 2803. The handover command may be based on one or moreelements of the third message. The fourth message may comprise some orall of the information in the third message. The fourth message may bean RRC connection reconfiguration message. The fourth message maycomprise, e.g., information associated with one or more cells served bya respective one or more base stations of a plurality of base stationsthat may comprise the target base station. Additionally oralternatively, the fourth message may comprise radio resourceconfiguration information (e.g., RACH configuration, channelconfiguration information, etc.) for the wireless device 2801, and/or amobility control information for the wireless device 2801. One or moreelements of the fourth message may be based on an acknowledgementreceived by the source base station from the target base station for thehandover request. The fourth message may comprise an indicationindicating that a random access for a handover execution is performedwith one of a two-step random access procedure and/or a four-step randomaccess procedure. The wireless device 2801 may receive and process thefourth message using the procedures described below regarding FIG. 34.

The wireless device 2801 may send, based on the random accessinformation in the fourth message, a fifth message that may be part of arandom access procedure with the target base station 2803, at step 2860.The wireless device 2801 may send a fifth message, e.g., comprising arandom access preamble, to the target base station 2803, e.g., via acell associated with the target base station 2803. The messagecomprising the random access preamble may be part of a random accessprocedure that may be performed with, e.g., two messages (e.g., fortwo-step random access) or four messages (e.g., for four-step randomaccess). The random access preamble may be transmitted in a first stepof one of a two-step random access procedure and/or a four-step randomaccess procedure. Timing advance information may be included in thefourth message. Timing advance information may comprise at least one ofan indication of a zero timing advance and/or a first value for a timingadvance. The first value of the timing advance may be estimated by thesource base station and/or the target base station. The fifth messagemay comprise, e.g., one or more transport blocks that may comprise atleast one of a handover complete message (e.g., an RRC connectionreconfiguration complete message), uplink data, a buffer status report,and/or an identifier of the wireless device (e.g., C-RNTI). The fourthmessage may comprise, e.g., a preamble identifier. Radio resources fortransmissions may be determined by the preamble identifier. The fourthmessage may comprise a random access channel configuration for atwo-step random access procedure and/or radio resource configurationparameters for a two-step random access procedure. The random accesspreamble may be transmitted in a first step of one of a two-step randomaccess procedure or a four-step random access procedure. Thetransmitting of the random access preamble message may be based on oneor more elements of the random access information included in the thirdmessage and/or the fourth message from steps 2840 and/or 2850,respectively. The type of random access procedure may be, e.g., atwo-step random access procedure or a four-step random access proceduredescribed further herein. The type of random access procedure may beindicated by the random access information in the fourth message,including, e.g., in a handover command. The random access information inthe fourth message may be the same as the random access information inthe third message. Additionally or alternatively, the random accessinformation in the fourth message may comprise additional informationprovided by the source base station 2802 and/or less than all of therandom access information included in the third message.

In a two-step random access procedure, a first random access message maybe transmitted by the wireless device 2801 to the target base station2803. The first random access message may comprise at least one of arandom access preamble, a radio resource control message, and/or one ormore uplink packets. A second random access message of a two-step randomaccess procedure may be transmitted to the wireless device 2801 by thetarget base station 2803, e.g., if the target base station 2803 receivesthe first random access message. The second random access message maycomprise, e.g., an acknowledgement of a reception of the first randomaccess message. The second random access message of the two-step randomaccess procedure may further comprise a resource grant for uplinkmessage transmission.

In a four-step random access procedure, a first random access messagemay be transmitted by the wireless device 2801 to the target basestation 2803, and the first random access message may comprise a randomaccess preamble. A second random access message of a four-step randomaccess procedure may be transmitted to the wireless device 2801 by thetarget base station 2803, e.g., if the target base station 2803 receivesthe first message. The second random access message may comprise aresource grant for uplink message transmission. A third random accessmessage of the four-step random access procedure may be transmitted bythe wireless device 2801 to the target base station 2803, at least basedon the resource grant in the second random access message. The thirdrandom access message may comprise a radio resource control messageand/or one or more uplink packets. A fourth random access message may betransmitted by the target base station 2803 to the wireless device 2801,and the fourth random access message may comprise an acknowledgement ofa reception of the third random access message. The fourth random accessmessage of the four-step random access procedure may further comprise aresource grant for uplink message transmission.

After completing the random access procedure initiated by the wirelessdevice 2801, the target base station 2803 may send a sixth message tonetwork device. The network device may comprise a core network entity.The sixth message may be transmitted to the network device, e.g., toupdate downlink packet destination information such as a tunnel endpointidentifier and/or an IP address and/or another address. The sixthmessage may comprise a path switch request message and/or a downlinkpacket destination information for one or more bearers for the wirelessdevice 2801. The network device may send a seventh message to the targetbase station 2803 that may be in response to the sixth message. Theseventh message may comprise a path switch request acknowledge message.Additionally or alternatively, the seventh message may comprise anuplink packet destination information, such as a tunnel endpointidentifier and/or an IP address and/or another address, for one or morebearers for the wireless device 2801, and/or a list of bearers to bereleased.

After completing a random access procedure initiated by the wirelessdevice 2801, the target base station 2803 may notify the source basestation 2802 that the handover has completed. The target base station2803 may notify the source base station 2802, e.g., by sending an eighthmessage to the source base station 2802. The eighth message may comprisea UE context release message and/or an identifier of the wireless device2801. The eighth message may be sent, e.g., via a direct interfacebetween the target base station 2803 and the source base station 2802.Additionally or alternatively, one or more elements of the eighthmessage may be sent to the source base station 2802 indirectly, e.g.,via one or more core network entities. In response to receiving theeighth message and/or the one or more elements of the eighth message,the source base station 2802 may release a wireless device context forthe wireless device 2801. Any one or more of the above describedmessages may be exchanged among one or more communication nodes betweenone or more of the wireless device 2801, the source base station 2802,and/or the target base station 2803.

FIG. 29 shows an example of a random access procedure for handover,e.g., using a core network device 2904. The core network device 2904 maybe located at a Next Generation Core (NGC) network entity that may beconfigured to communicate, e.g., via an NG interface, with one or bothof the source base station 2902 and the target base station 2903. One ormore of a wireless device 2901, a source base station 2902 (e.g., aneNB, a gNB, etc.), and/or a target base station 2903 (e.g., an eNB, agNB, etc.), and operations thereof, may correspond to the wirelessdevice 2801, the source base station 2802, and/or the target basestation 2803, respectively, described above regarding FIG. 28,descriptions of which are incorporated herein with respect to FIG. 29.The messages sent in steps 2810, 2830, 2840, 2850, and 2860 of FIG. 28may correspond to messages sent in similarly numbered steps 2910, 2930,2940, 2950, and 2960, respectively, of FIG. 29. The handover decision instep 2820 of FIG. 28 may also correspond to the handover decision instep 2920 of FIG. 29.

The core network device 2904 may communicate with the source basestation 2902 and the target base station 2903. The core network device2904 may comprise one or more devices located at a core network entity,such as an NGC, one or more devices at an access and mobility managementfunction (AMF) network entity, one or more devices at a mobilitymanagement entity (MME), or one or more devices at any other location.The core network device 2904 may determine an availability of basestations, including a determining whether a target base station, such asthe target base station 2903, is available. The core network device 2904may communicate with the source base station 2902 and the target basestation 2903 via an NG interface and/or via an S1 interface (e.g., foran MME), and the core network device 2904 may operate as an intermediaryfor communications between the source base station 2902 and the targetbase station 2903. Processing in the core network device 2904, andpotential latency in communicating information to and from the corenetwork device 2904, may not delay a handover when, e.g., some or all ofsuch processes and communications may occur prior to a handover.

At step 2910 the wireless device 2901 may send, to a source base station2902, a first message comprising a measurement report for one or morecells, including, e.g., a cell for the target base station 2903. Thefirst message in step 2910 may comprise some or all of the informationin the first message in step 2810 described above. The wireless devicemay generate the measurement report using the procedures described belowregarding FIG. 30.

The source base station 2902 may receive the first message at step 2910.At step 2920, the source base station 2902 may make a handover decision.The handover decision may be based on the measurement report in thefirst message. The handover decision may also be based on adetermination whether to use a core network device 2904 for a handover.As an example, if an Xn connection is established between the sourcebase station 2902 and the target base station 2903, the source basestation 2902 may determine to send a second message, e.g., comprising ahandover request, to the target base station 2903 without involving thecore network device 2904; and if an Xn connection is not establishedbetween the source base station 2902 and the target base station 2903,then the source base station 2902 may send a second message, e.g.,comprising a handover required message, to the core network device 2904at step 2925. The second message may be based on the measurement report.The second message (e.g., a handover request message and/or a handoverrequired message) may further comprise one or more measurements resultsof a measurement report (e.g., that may be provided by the wirelessdevice step 2810) and/or one or more of: timing advance information fortransmission of uplink data, a random access preamble, and/or randomaccess information. The second message in step 2925 may comprise some orall of the information in the second message in step 2830 describedabove. The source base station 2902 may perform the handover decision instep 2920, and receive and send the first and second messages in steps2910 and 2925, respectively, using the procedures described belowregarding FIG. 31.

The core network device 2904 may receive the second message at step2925. The core network device 2904 may process the second message,including, e.g., to determine whether the wireless device may requirelatency sensitive service. The core network device 2904 may determinewhether the wireless device may require latency sensitive service basedon, e.g., packet data unit session information of the wireless device.At step 2930, the core network device 2904 may send, to the target basestation 2903, a third message comprising a handover request. The thirdmessage in step 2930 may comprise some or all of the information in thesecond message in step 2830 described above. The core network device2904 may receive and process the second message in step 2925, anddetermine and send the third message in step 2930, using the proceduresdescribed below regarding FIG. 33.

The target base station 2903 may receive the third message at step 2930.The target base station 2903 may determine whether the handover requestis acceptable. The target base station 2903 may process a handoverrequest in a direct handover from a source base station 2902, e.g., viaan Xn interface, using one or more of the same procedures as the targetbase station 2903 uses to process a handover request from a core networkdevice 2904, e.g., via an NG interface. The target base station 2903 mayalso determine characteristics that may be relevant for a handover, suchas power, latency sensitive service type, cell size, and/or availabilityof one or more types of random access procedures. Based on one or moredeterminations, at step 2940, the target base station 2903 may send, tothe core network device 2904, a fourth message comprising a handoverrequest acknowledgement and random access information. The fourthmessage in step 2940 may comprise some or all of the information in thethird message in step 2840 described above. The target base station 2903may receive and process the third message in step 2930, and determineand send the fourth message in step 2940, using the procedures describedbelow regarding FIG. 32.

The core network device 2904 may receive the fourth message at step2940. The core network device 2904 may process the fourth message togenerate a fifth message comprising a handover request acknowledgementand random access information. At step 2945, the core network device2904 may send the fourth message to the source base station 2902. Thefifth message in step 2945 may comprise some or all of the informationin the third message in step 2840 described above. The core networkdevice 2904 may receive and process the fourth message in step 2940, anddetermine and send the fifth message in step 2945, using the proceduresdescribed below regarding FIG. 33.

The source base station 2902 may receive the fifth message at step 2945.The source base station 2902 may process the fifth message to determinea sixth message, e.g., comprising a handover command and random accessinformation. At step 2950, the source base station may send, to thewireless device 2901, the sixth message. The sixth message in step 2950may comprise some or all of the information in the fourth message instep 2850 described above. The source base station 2902 may receive andprocess the fifth message in step 2945, and determine and send the sixthmessage in step 2950, using procedures described below regarding FIG.31.

The wireless device 2901 may receive, from the source base station 2902,the sixth message at step 2950. The sixth message may comprise ahandover command and random access information. The handover command maycomprise a command for a handover a cell of the source base station 2902to a cell of the target base station 2903. At step 2960, the wirelessdevice 2901 may obtain channel access by proceeding with a random accessprocedure with the target base station 2903. The wireless device 2901may initiate the random access procedure by sending, to the target basestation 2903, a seventh message comprising a random access preamble anddata. The wireless device may transmit, to the target base station 2903,one or more transport blocks via radio resources of the cell of thetarget base station 2903, wherein the radio resources may be determinedat least based on one or more elements of the sixth message. Thetransmitting, by the wireless device 2901, may further comprisetransmitting a random access preamble overlapping in time withtransmission of the one or more transport blocks. The sixth message maycomprise, e.g., an indication for performing a two-step random accessprocedure, and/or a preamble identifier for a two-step random accessprocedure. The seventh message may comprise some or all of theinformation in step 2003 of the two-step random access proceduredescribed above regarding FIG. 20. The wireless device 2901 may receiveand process the sixth message in step 2950, and determine and send theseventh message in step 2960, using the procedures described belowregarding FIG. 34.

FIG. 30 shows an example of handover procedures 3000 for a wirelessdevice. The procedures may start with step 3001 during which a wirelessdevice, such as the wireless device 2801 and/or the wireless device2901, measures target cell quality and serving cell quality. Thewireless device may also measure cell quality of one or more neighboringcells that may become a target cell. The wireless device may makemeasurements to determine power of transmissions from one or more basestations in a respective one or more neighboring cells. The wirelessdevice may also measure the power of transmissions by a source basestation, such as the source base station 2802 and/or the source basestation 2902, that may be serving the wireless device. At step 3002, thewireless device may determine whether one or more measurement eventshave occurred. A measurement event may be an indication that a targetcell quality may exceed a serving cell quality and/or may exceed aserving cell quality by an offset value. A measurement event maycomprise, e.g., one or more of a determination that an RSRP and/or anRSRQ of a target cell (e.g., a cell of a target base station) is greaterthan a first threshold; a determination that an RSRP and/or an RSRQ of asource cell (e.g., a cell of a source base station) is less than asecond threshold; a determination that an RSRP and/or an RSRQ of atarget cell exceeds a an RSRP and/or RSRQ of a source cell and/orexceeds an RSRP and/or RSRQ of a source cell by an offset power value;and/or a determination that a time duration of maintaining a condition,such as one or more of the above conditions, is greater than or equal toa time threshold value. If the wireless device determines that one ormore measurement events have not occurred, the wireless device mayreturn to step 3001. If the wireless device determines that one or moremeasurement events have occurred, then the wireless device may send ameasurement report to the source base station at step 3003, such asdescribed above regarding step 2810 in FIG. 28 and/or step 2910 in FIG.29. The wireless device may receive a handover command and RAinformation from a source base station at step 3004, such as describedabove regarding step 2850 in FIG. 28 and/or step 2950 in FIG. 29. Thehandover command and/or RA information may comprise an indication of atype of RA procedure that the wireless device is to perform for ahandover to a target base station. The wireless device may proceed witha RA procedure for channel access with the target base station. The RAprocedure may be based on the handover command and RA informationreceived from the source base station. The process 3000 may end afterstep 3005, or the process 3000 may repeat after a time period or afteran event that may trigger a measurement of target cell quality and/orserving cell quality, such as one or more indications of a transmissionfailure and/or one or more indications of a neighbor cell transmission.

One or more additional steps (not shown) may also be performed by thewireless device, in between, before, or after, any of steps 3001-3005,e.g., to determine whether to initiate a handover, and/or to determine atype of RA procedure to use. Such additional steps may include powermeasurements, distance measurements, traffic measurements, moving speedof the wireless devices, determination of other cells available to thewireless device, and any other network condition that may be used todetermine a handover and/or a type of RA procedure.

FIG. 31 shows an example of handover procedures 3100 for a source basestation. The procedures may start with step 3101 during which a sourcebase station, such as the source base station 2802 and/or the sourcebase station 2902, receives a measurement report from a wireless device.Based on the measurement report, the source base station may determine,at step 3102, whether one or more handover triggering condition havebeen satisfied. The one or more handover triggering conditions maycomprise some or all of the measurement events described above in step3002 of FIG. 30. Additionally or alternatively, the one or more handovertriggering conditions may comprise a determination that an RSRP and/orRSRQ of a target cell indicates better performance for a wireless devicethan an RSRP and/or RSRQ of other candidate target cells; adetermination that a moving speed of a wireless device is slower than athreshold speed value; and/or a cell identifier of a target cell is, oris not, among one or more cells in a handover restriction. If the sourcebase station determines that one or more handover triggering conditionshave not occurred, the source base station may end the process 3100. Ifthe source base station determines that one or more handover triggeringconditions have occurred, then the source base station may proceed tostep 3103.

The source base station may determine, at step 3103, whether to proceedwith handover procedures via direct communications (e.g., employing anXn interface) with a target base station, or via indirect communicationswith a target base station, e.g., using a core network device such as2904 as an intermediary. The source base station may base itsdetermination of direct or indirect communications with the target basestation on the type of connection it may have with the target basestation. If the source base station and the target base station arecapable of sufficiently timely direct communications with each other,such as via an Xn interface, then the source base station may determineto proceed with direct communications with the target base station,e.g., via steps 3104 and 3105, and/or via the process described aboveregarding FIG. 28. If the source base station and the target basestation are not capable of sufficiently timely direct communicationswith each other, such as via an Xn interface (e.g., if these two basestations only communicate with each other via an X2 interface or if anX2 interface between these two base stations is not operatingsufficiently to accommodate sufficiently timely communications), thenthe source base station may determine to proceed with indirectcommunications with the target base station, e.g., via steps 3106 and3107, and/or via the process described above regarding FIG. 29.

At step 3104, a source base station may send a handover request messageto a target base station, as described above regarding step 2830. Atstep 3105, the source base station may receive a handover requestacknowledgement and RA information, as described above regarding step2840. At step 3106, a source base station may send a handover requiredmessage to a core network device, such as core network device 2904, asdescribed above regarding step 2925. At step 3107, the source basestation may receive a handover required acknowledgement and RAinformation, as described above regarding step 2945. After step 3105and/or after step 3107, the process may continue to step 3108. At step3108, the source base station may process the handover requestacknowledgement and/or RA information, and the source base station maysend a handover command and RA information to the wireless device forhandover to the target base station, as described above regarding step2850. The process 3100 may end after step 3108.

One or more of steps 3102-3103 may be omitted, or performed before orafter other steps. Additional steps (not shown) may also be performed bythe source base station, in between, before, or after, any of steps3102-3103, e.g., to determine whether to initiate a handover of thewireless device, to determine whether to send one or morehandover-related messages to a target base station and/or to a corenetwork device, and/or to determine a type of RA procedure. Suchadditional steps may include power measurements, distance measurements,service type measurements (e.g., slice type, packet data unit sessiontype, QoS flow type, bearer type, and/or QoS requirement), trafficmeasurements, moving speed of the wireless devices, determination ofother cells available to the wireless device, and any other networkcondition that may be used to determine a handover and/or a type of RAprocedure.

FIG. 32 shows an example of handover procedures 3200 for a target basestation. The procedures may start with step 3201 during which a targetbase station, such as the target base station 2803 and/or the targetbase station 2903, receives a handover request message for a wirelessdevice. Based on the handover request message, the target base stationmay determine, at step 3202, whether the handover request is acceptable.The determination of whether the handover request is acceptable may bebased on one or more of: whether radio resources are available for atleast a default packet data unit session of the wireless device; whethera particular one or more service type are supported at the target cell;whether an RSRP and/or an RSRQ satisfies a threshold; whether a movingspeed of the wireless device is below a speed threshold; and/or whethera cause for the handover is reasonable, such as to provide emergencyservice or to reduce traffic load of a source cell (e.g., if an RSRPand/or RSRQ does not satisfy a threshold). If a determination is madethat the handover request is not acceptable, then the process maycontinue to step 3203 and the target base station may send a handoverfailure message, after which the process 3200 may end. If adetermination is made that the handover request is acceptable, then theprocess may continue to step 3204.

At step 3204, the target base station may determine whether RSRP exceedsa power threshold. If RSRP exceeds a power threshold, the process maycontinue to step 3205, in which case the target base station may send ahandover request acknowledgement message indicating a four-step randomaccess procedure for handover. A four-step random access procedure mayuse less power per transmission than a two-step random access procedure,e.g., because a two-step random access procedure may transmit moreinformation in each step relative to a four-step random accessprocedure. If RSRP does not exceed a power threshold, the process maycontinue to step 3206.

At step 3206, the target base station may determine whether the wirelessdevice requires latency sensitive service, such as for emergency orother time-sensitive messages. If the target base station determinesthat the wireless device does not require latency sensitive service, thetarget base station may determine, at step 3207, whether the size of thehandover target cell is small, or below a threshold size (e.g., a timealignment may less (or not) affect communication between the target basestation and the wireless device). If the target base station determinesthat the size of the target cell is below a threshold size, the targetbase station may determine, at step 3208, whether the wireless devicesupports a two-step RA procedure (e.g., based on UE capabilityinformation of the wireless device in the handover request message). Ifthe target base station determines that the wireless device supports atwo-step RA procedure, the target base station may determine, at step3209, whether one or more random access resources for two-step RA areavailable at the target cell. If the target base station determines thateach condition in steps 3204-3209 is satisfied, the target base stationmay send, at step 3210, a handover request acknowledgement message(e.g., to the source base station 2802 in step 2840 FIG. 28 and/or tothe core network device 2904 in step 2940 FIG. 29) indicating a two-stepRA procedure for the handover. If the target base station determines anyone or more of the conditions in steps 32094-3209 are not satisfied, thetarget base station may send, at step 3205, a handover requestacknowledgement (e.g., to the source base station 2802 in step 2840 FIG.28 and/or to the core network device 2904 in step 2940 FIG. 29)indicating a four-step RA procedure for the handover. After sending ahandover request acknowledgement message, in step 3205 or in step 3210,the target base station may proceed with a RA procedure (e.g., as instep 2860 in FIG. 28 and/or as in step 2960 in FIG. 29) with thewireless device for channel access, in step 3211 (e.g., by receiving acorresponding RA preamble from the wireless device). The process 3200may end after step 3211.

One or more of steps 3204-3209 may be omitted, or performed before orafter any of the other steps 3204-3209. Additional steps (not shown) mayalso be performed by the target base station, in between, before, orafter, any of steps 3204-3209, to determine whether to indicate, in ahandover request acknowledgement, a four-step RA procedure or a two-stepRA procedure. Such additional steps may include power measurements,distance measurements, traffic measurements, moving speed of thewireless devices, determination of other cells available to the wirelessdevice, and any other network condition that may be used to determine ahandover and/or a type of RA procedure.

FIG. 33 shows an example of handover procedures 3300 for a core networkdevice. The procedures may start with step 3301 during which a corenetwork device, such as the core network device 2904 in FIG. 29,receives a handover required message from a source base station (e.g., amessage in step 2925 in FIG. 29). At step 3302, the core network devicemay determine whether the wireless device requires latency sensitiveservice, such as for emergency or other time-sensitive messages. Thecore network device 2904 may determine whether the wireless devicerequires latency sensitive service based on, e.g., packet data unitsession information of the wireless device. If latency services are notrequired, the process may continue to step 3304. If latency services arerequired by the wireless device, then at step 3303, the core networkdevice may include a latency sensitive service indication in a handoverrequest message, before continuing to step 3304. At step 3304, the corenetwork device may send a handover request message to a target basestation (e.g., as in step 2930 in FIG. 29). At step 3305, the corenetwork device may receive a handover request acknowledgement and randomaccess information from the target base station (e.g., as in step 2940in FIG. 29). At step 3306, the core network device may send a handoverrequired acknowledgement and random access information to the sourcebase station (e.g., as in step 2945). The process 3300 may end afterstep 3306.

One or more additional steps (not shown) may also be performed by thecore network device, in between, before, or after, any of steps3301-3305, e.g., to determine whether to send one or more handovermessages, to determine what to include in one or more handover messages,and/or to determine a type of RA procedure to indicate in one or morehandover messages. Such additional steps may include power measurements,distance measurements, traffic measurements, moving speed of thewireless devices, determination of other cells available to the wirelessdevice, and any other network condition that may be used to determine ahandover and/or a type of RA procedure.

FIG. 34 shows an example of handover procedures 3400 for a wirelessdevice. The procedures may start with step 3401 during which a wirelessdevice, such as the wireless device 2801 and or the wireless device2901, receives a handover command message from a source base station(e.g., as in step 2850 in FIG. 28 and/or as in step 2950 in FIG. 29).The handover command message may comprise random access information. Atstep 3402, the wireless device may determine, based on the random accessinformation, whether the handover command message indicates a two-steprandom access procedure. If the wireless device determines that atwo-step random access procedure is indicated, the wireless device, atstep 3404, may send to a target base station a random access preamblefor a two-step RA procedure. If the wireless device determines that atwo-step random access procedure is not indicated in the handovercommand message, then the wireless device, at step 3403, may send to thetarget base station a random access preamble for a four-step RAprocedure. After sending a random access preamble, the wireless devicemay continue with the particular random access procedure (e.g., atwo-step RA procedure or a four-step RA procedure) at step 3405 (e.g.,as in step 2860 in FIG. 28 and/or as in step 2960 in FIG. 29). Theprocess 3400 may end after step 3405.

One or more additional steps (not shown) may also be performed by thewireless device, in between, before, or after, any of steps 3401-3405,e.g., to determine whether to proceed with a handover, to determine oneor more RA transmissions, and/or to determine a type of RA procedure touse. Such additional steps may include power measurements, distancemeasurements, traffic measurements, moving speed of the wirelessdevices, determination of other cells available to the wireless device,and any other network condition that may be used to determine a handoverand/or a type of RA procedure.

A wireless device may perform a method for determining a type of randomaccess procedure to use for a handover from a source base station to atarget base station. The wireless device may receive, from one or morecells, a plurality of messages comprising one or more of an indicationof a power associated with a cell, an indication of a quality associatedwith a cell, and/or an indication of a cell priority. The wirelessdevice may determine, based on the plurality of messages, a measurementreport. The wireless device may transmit, to a first base station, afirst message comprising a measurement report based on one or moresecond cells. The wireless device may receive, from the first basestation, a second message comprising a command for a handover from thefirst cell to a second cell of the one or more second cells. The firstcell may be a source cell for the wireless device, and the second cellmay be a target cell. The second message may comprise one or moreparameters indicating a type of a random access procedure for thehandover. Additionally or alternatively, the second message may comprisetiming advance information, e.g., for transmission of one or more uplinkdata and/or a random access preamble. The timing advance information maycomprise one or more of an indication of a zero timing advance, or avalue for a timing advance. The value for the timing advance may beestimated by the first base station and/or the second base station. Oneor more elements of the second message may be based on anacknowledgement received by the first base station, from the second basestation, for the handover request. For a two-step random accessprocedure, the second message may comprise one or more of a preambleidentifier for the RA procedure, random access channel configurationinformation for the RA procedure, random access resource information forthe RA procedure, or radio resource configuration parameters. Thewireless device may determine, based on the preamble identifier, radioresources to use for the RA procedure. For a four-step random accessprocedure, the second message may comprise a root sequence that thewireless may use to generate a random access preamble that the wirelessdevice may transmit in a first step of the four-step RA procedure. Thetype of the random access procedure may comprise a two-step randomaccess procedure or a four-step random access procedure. The wirelessdevice may transmit, to the second base station, a random accesspreamble employing the type of random access procedure indicated in thesecond message. The wireless device may transmit, to the second basestation, one or more transport blocks. The one or more transport blocksmay comprise one or more of a handover complete message, uplink data, abuffer status report, or an identifier of the wireless device. Thewireless device may transmit, to the second base station, a randomaccess preamble overlapping in time with the one or more transportblocks. The wireless device may transmit, in a first step of a four-steprandom access procedure, a second random access preamble. A wirelessdevice may perform any combination of one or more of the above steps. Abase station, or any other device, may perform any combination of astep, or a complementary step, of one or more of the above steps.

A first base station may perform a method for indicating a type ofrandom access procedure in a handover from the first base station (e.g.,a source base station) to a second base station (e.g., a target basestation). The first base station may receive, from a wireless device, afirst message comprising a measurement report based on one or moresecond cells. The first base station may be associated with a firstcell. The first base station may determine, based on the measurementreport, to handover the wireless device from the first cell to a secondcell of the one or more second cells. The first cell may be a sourcecell for the wireless device, and the second cell may be a target cell.The first base station may transmit, to a third device, a second messagecomprising an indication for the handover. The third device may comprisethe second base station that may be associated with the second cell.Additionally or alternatively, the third device may comprise a corenetwork device. The third device may determine the second cell from aplurality of cells. The second message may comprise a handover requestand/or an indication that a handover is requested. The first basestation may receive, from the third device, a third message indicating atype of a random access procedure for the handover. The type of therandom access procedure may comprise a two-step random access procedureor a four-step random access procedure. The first base station maytransmit, to the wireless device, a fourth message. The fourth messagemay comprise one or more parameters indicating the type of the randomaccess procedure for the handover and/or the fourth message may comprisea command to proceed with the handover. The fourth message may comprisetiming advance information, e.g., for transmission of one or more uplinkdata or a random access preamble. The timing advance information maycomprise one or more of an indication of a zero timing advance, or avalue for a timing advance. The value for the timing advance may beestimated by the first base station and/or the third device. For atwo-step random access procedure, the fourth message may comprise apreamble identifier for the RA procedure. The third device may transmit,to a second base station and based on the second message, a fifthmessage comprising a handover request. The third device may receive,from the second base station, a sixth message indicating the type of therandom access procedure for the handover and comprising anacknowledgement of the handover request. One or more base stations(e.g., a source base station, a target base station, etc.) may performany combination of one or more of the above steps. A wireless device, acore network device, or any other device, may perform any combination ofa step, or a complementary step, of one or more of the above steps.

A network device may perform a method for indicating a type of randomaccess procedure in a handover from a first base station (e.g., a sourcebase station 2902) to a second base station (e.g., a target base station2903). The network device may comprise a core network device (e.g., corenetwork device 2904). Additionally or alternatively, the network devicemay comprise the second base station. The network device may receive,from a first base station, a first message comprising an indication fora handover of a wireless device from a first cell associated with thefirst base station to a second cell of one or more second cells. Thesecond base station may be associated with the second cell. The firstcell may be a source cell for the wireless device, and the second cellmay be a target cell. The network device may determine the second cellfrom a plurality of cells. The network device may determine, based onthe first message, to proceed with the handover. The network device maytransmit, to the first base station a second message. The second messagemay comprise one or more of an acknowledgement for the handover, ahandover request, an indication that a handover is required, or anindication of a type of a random access procedure for the handover. Thetype of the random access procedure may comprise a two-step randomaccess procedure or a four-step random access procedure. The networkdevice may transmit, to a second base station and based on the firstmessage, a third message comprising a handover request. The networkdevice may receive, from the second base station, a fourth message. Thefourth message may indicate the type of the random access procedure forthe handover. The fourth message may comprise an acknowledgement of thehandover request. One or more network devices may perform anycombination of one or more of the above steps. A wireless device, a basestation, or any other device, may perform any combination of a step, ora complementary step, of one or more of the above steps.

One or more of the messages described herein may be exchanged among oneor more devices at a communication node in a network. One or more of theprocesses described herein may be performed in one or more devices in anetwork. For example, if an interface between a target base station(e.g., the target base station 2903) and a source base station (e.g.,the source base station 2902) cannot accommodate sufficiently timelycommunications, such as if the interface between these base stations isnot an Xn interface of if an X2 interface between them is not operative,a core network device (e.g., the core network device 2904) may be usedto perform handover processes and send and receive handover relatedmessages described herein with respect to a target base station and/or asource base station. As another example, if a wireless device (e.g., thewireless device 2801 and/or the wireless device 2901) is a fast movingdevice, a source base station (e.g., the source base station 2801 and/orthe source base station 2902) may be used to perform handover processesand send and receive handover related messages described herein withrespect to a target base station and/or a core network device. Asanother example, if a wireless device (e.g., the wireless device 2801and/or the wireless device 2901) has latency sensitive information, suchas emergency information, and if a source base station cannotaccommodate the wireless device transmissions and cannot perform ahandover decision in a sufficiently timely manner, the wireless devicemay perform handover processes and send and receive handover relatedmessages described herein with respect to a source base station, atarget base station, and/or a core network device.

Many of the elements in examples may be implemented as modules. A modulemay be an isolatable element that performs a defined function and has adefined interface to other elements. The modules may be implemented inhardware, software in combination with hardware, firmware, wetware(i.e., hardware with a biological element) or a combination thereof, allof which may be behaviorally equivalent. For example, modules may beimplemented as a software routine written in a computer languageconfigured to be executed by a hardware machine (such as C, C++,Fortran, Java, Basic, Matlab or the like) or a modeling/simulationprogram such as Simulink, Stateflow, GNU Octave, or Lab VIEWMathScript.Additionally or alternatively, it may be possible to implement modulesusing physical hardware that incorporates discrete or programmableanalog, digital and/or quantum hardware. Examples of programmablehardware may comprise: computers, microcontrollers, microprocessors,application-specific integrated circuits (ASICs); field programmablegate arrays (FPGAs); and complex programmable logic devices (CPLDs).Computers, microcontrollers, and microprocessors may be programmed usinglanguages such as assembly, C, C++ or the like. FPGAs, ASICs, and CPLDsmay be programmed using hardware description languages (HDL), such asVHSIC hardware description language (VHDL) or Verilog, that mayconfigure connections between internal hardware modules with lesserfunctionality on a programmable device. The above mentioned technologiesmay be used in combination to achieve the result of a functional module.

Systems, apparatuses, and methods may perform operations ofmulti-carrier communications described herein. Additionally oralternatively, a non-transitory tangible computer readable media maycomprise instructions executable by one or more processors configured tocause operations of multi-carrier communications described herein. Anarticle of manufacture may comprise a non-transitory tangible computerreadable machine-accessible medium having instructions encoded thereonfor enabling programmable hardware to cause a device (e.g., a wirelesscommunicator, a UE, a base station, and the like) to enable operation ofmulti-carrier communications described herein. The device, or one ormore devices such as in a system, may include one or more processors,memory, interfaces, and/or the like. Other examples may comprisecommunication networks comprising devices such as base stations,wireless devices or user equipment (UE), servers, switches, antennas,and/or the like. Any device (e.g., a wireless device, a base station, orany other device) or combination of devices may be used to perform anycombination of one or more of steps described herein, including, e.g.,any complementary step or steps of one or more of the above steps.

Although examples are described above, features and/or steps of thoseexamples may be combined, divided, omitted, rearranged, revised, and/oraugmented in any desired manner Various alterations, modifications, andimprovements will readily occur to those skilled in the art. Suchalterations, modifications, and improvements are intended to be part ofthis description, though not expressly stated herein, and are intendedto be within the spirit and scope of the disclosure. Accordingly, theforegoing description is by way of example only, and is not limiting.

The invention claimed is:
 1. A wireless device comprising: one or moreprocessors; and memory storing instructions that, when executed by theone or more processors, cause the wireless device to: transmit, to afirst base station associated with a first cell, a first messagecomprising a measurement report based on one or more second cells;receive, from the first base station, a second message comprising acommand for a handover from the first cell to a second cell of the oneor more second cells, wherein the second message comprises one or moreparameters indicating a type of a random access procedure for thehandover, and wherein the type of the random access procedure comprisesa two-step random access procedure or a four-step random accessprocedure; and transmit, to a second base station associated with thesecond cell, a random access preamble employing the type of the randomaccess procedure indicated in the second message.
 2. The wireless deviceof claim 1, wherein the instructions, when executed by the one or moreprocessors, further cause the wireless device to: transmit one or moretransport blocks overlapping in time with the random access preamble. 3.The wireless device of claim 2, wherein the one or more transport blockscomprise one or more of: a handover complete message; uplink data; abuffer status report; or an identifier of the wireless device.
 4. Thewireless device of claim 1, wherein the one or more parameters of thesecond message comprise, for the random access procedure, one or moreof: a preamble identifier; or random access resource information.
 5. Thewireless device of claim 1, wherein the second message furthercomprises: timing advance information for transmission of one or more ofthe random access preamble or one or more transport blocks.
 6. Thewireless device of claim 5, wherein the instructions, when executed bythe one or more processors, further cause the wireless device to:receive, from the one or more second cells, a plurality of thirdmessages comprising one or more of: an indication of a power associatedwith a cell; an indication of a quality associated with a cell; or anindication of a cell priority.
 7. The wireless device of claim 1,wherein the instructions, when executed by the one or more processors,further cause the wireless device to: transmit, in a first step of afour-step random access procedure, a second random access preamble. 8.The wireless device of claim 1, wherein the instructions, when executedby the one or more processors, further cause the wireless device to:determine, based on a preamble identifier in the second message, radioresources associated with the random access procedure.
 9. The wirelessdevice of claim 1, wherein the second message comprises: random accesschannel configuration information for a two-step random accessprocedure; and radio resource configuration parameters for the two-steprandom access procedure.
 10. A base station, associated with a firstcell, comprising: one or more processors; and memory storinginstructions that, when executed by the one or more processors, causethe base station to: receive, from a wireless device, a first messagecomprising a measurement report based on one or more second cells;transmit, to a computing device, a second message comprising anindication of a handover of the wireless device to a second cell of theone or more second cells; receive, from the computing device, a thirdmessage indicating a type of a random access procedure for the handover,wherein the type of the random access procedure comprises a two-steprandom access procedure or a four-step random access procedure; andtransmit, to the wireless device, a fourth message, associated with thehandover, that comprises one or more parameters indicating the type ofthe random access procedure for the handover.
 11. The base station ofclaim 10, wherein: the computing device comprises a second base stationassociated with the second cell; and the second message comprises ahandover request.
 12. The base station of claim 10, wherein: thecomputing device comprises a core network device; and the second messageindicates that the handover is requested.
 13. The base station of claim10, wherein the one or more parameters of the fourth message comprise,for the random access procedure, one or more of: a preamble identifier;or random access resource information.
 14. The base station of claim 10,wherein the fourth message further comprises timing advance informationfor transmission of one or more of a random access preamble or one ormore transport blocks.
 15. The base station of claim 14, wherein thetiming advance information comprises one or more of: an indication of azero timing advance; or a value for a timing advance, wherein the valueis estimated by the base station or a computing device.
 16. A methodcomprising: receiving, by a base station associated with a first celland from a wireless device, a first message comprising a measurementreport based on one or more second cells; transmitting, to a computingdevice, a second message comprising an indication of a handover of thewireless device to a second cell of the one or more second cells;receiving, from the computing device, a third message indicating a typeof a random access procedure for the handover, wherein the type of therandom access procedure comprises a two-step random access procedure ora four-step random access procedure; and transmitting, to the wirelessdevice, a fourth message, associated with the handover, that comprisesone or more parameters indicating the type of the random accessprocedure for the handover.
 17. The method of claim 16, wherein: thecomputing device comprises a second base station associated with thesecond cell; and the second message comprises a handover request. 18.The method of claim 16, wherein: the computing device comprises a corenetwork device; and the second message indicates that the handover isrequested.
 19. The method of claim 18, further comprising: transmitting,by the core network device, to a second base station, and based on thesecond message, a fifth message comprising a handover request; andreceiving, by the core network device and from the second base station,a sixth message indicating the type of the random access procedure forthe handover and comprising an acknowledgement of the handover request.20. The method of claim 16, wherein the one or more parameters of thefourth message comprise, for the random access procedure, one or moreof: a preamble identifier; or random access resource information. 21.The method of claim 16, wherein the fourth message further comprisestiming advance information for transmission, by the wireless device, ofone or more of a random access preamble or one or more transport blocks.22. The method of claim 21, wherein the timing advance informationcomprises one or more of: an indication of a zero timing advance; or avalue for a timing advance, wherein the value is estimated by the basestation or a computing device.
 23. A computing device comprising: one ormore processors; and memory storing instructions that, when executed bythe one or more processors, cause the computing device to: receive, froma first base station associated with a first cell, a first messagecomprising an indication for a handover of a wireless device from thefirst cell to a second cell of one or more second cells; and transmit,to the first base station and based on a determination to proceed withthe handover, a second message that comprises one or more parametersindicating a type of a random access procedure for the handover, whereinthe type of the random access procedure comprises a two-step randomaccess procedure or a four-step random access procedure.
 24. Thecomputing device of claim 23, wherein the second message comprises ahandover request.
 25. The computing device of claim 23, wherein thesecond message comprises an indication that the handover is required.26. The computing device of claim 25, wherein the instructions, whenexecuted by the one or more processors, further cause the computingdevice to: transmit, to a second base station and based on the firstmessage, a third message comprising a handover request; and receive,from the second base station, a fourth message comprising a handoverrequest acknowledgement that indicates the type of the random accessprocedure for the handover.
 27. The computing device of claim 26,wherein the fourth message is received based on a determination, by thesecond base station, that the handover request is acceptable.
 28. Thecomputing device of claim 23, wherein the computing device comprises atleast one of: a core network device; or a second base station associatedwith the second cell.
 29. A method comprising: receiving, by a networkdevice and from a first base station associated with a first cell, afirst message comprising an indication for a handover of a wirelessdevice from the first cell to a second cell of one or more second cells;and based on a determination to proceed with the handover, transmitting,to the first base station, a second message, associated with thehandover, that comprises one or more parameters indicating a type of arandom access procedure for the handover, wherein the type of the randomaccess procedure comprises a two-step random access procedure or afour-step random access procedure.
 30. The method of claim 29, wherein:the network device comprises a second base station that is associatedwith the second cell; and the second message comprises a handoverrequest.
 31. The method of claim 29, wherein: the network devicecomprises a core network device; and the second message comprises anindication that the handover is required.
 32. The method of claim 31,further comprising: transmitting, by the core network device, to asecond base station, and based on the first message, a third messagecomprising a handover request; and receiving, by the core network deviceand from the second base station, a fourth message indicating the typeof the random access procedure for the handover and comprising anacknowledgement of a request for a handover request.
 33. The method ofclaim 29, further comprising: receiving, from a second base stationassociated with the second cell, a handover acknowledgment indicatingproceeding with the handover.
 34. A non-transitory computer-readablemedium storing instructions that, when executed by one or moreprocessors of a wireless device, cause the wireless device to: transmit,to a first base station associated with a first cell, a first messagecomprising a measurement report based on one or more second cells;receive, from the first base station, a second message comprising acommand for a handover from the first cell to a second cell of the oneor more second cells, wherein the second message comprises one or moreparameters indicating a type of a random access procedure for thehandover, and wherein the type of the random access procedure comprisesa two-step random access procedure or a four-step random accessprocedure; and transmit, to a second base station associated with thesecond cell, a random access preamble employing the type of the randomaccess procedure indicated in the second message.
 35. The non-transitorycomputer-readable medium of claim 34, wherein the instructions, whenexecuted by the one or more processors, further cause the wirelessdevice to: transmit one or more transport blocks overlapping in timewith the random access preamble.
 36. The non-transitorycomputer-readable medium of claim 35, wherein the one or more transportblocks comprise one or more of: a handover complete message; uplinkdata; a buffer status report; or an identifier of the wireless device.37. The non-transitory computer-readable medium of claim 34, wherein theone or more parameters of the second message comprise, for the randomaccess procedure, one or more of: a preamble identifier; or randomaccess resource information.
 38. The non-transitory computer-readablemedium of claim 34, wherein the second message further comprises: timingadvance information for transmission of one or more of the random accesspreamble or one or more transport blocks.
 39. The non-transitorycomputer-readable medium of claim 38, wherein the instructions, whenexecuted by the one or more processors, further cause the wirelessdevice to: receive, from the one or more second cells, a plurality ofthird messages comprising one or more of: an indication of a powerassociated with a cell; an indication of a quality associated with acell; or an indication of a cell priority.
 40. The non-transitorycomputer-readable medium of claim 34, wherein the instructions, whenexecuted by the one or more processors, further cause the wirelessdevice to: transmit, in a first step of a four-step random accessprocedure, a second random access preamble.
 41. The non-transitorycomputer-readable medium of claim 34, wherein the instructions, whenexecuted by the one or more processors, further cause the wirelessdevice to: determine, based on a preamble identifier in the secondmessage, radio resources associated with the random access procedure.42. The non-transitory computer-readable medium of claim 34, wherein thesecond message comprises: random access channel configurationinformation for a two-step random access procedure; and radio resourceconfiguration parameters for the two-step random access procedure.
 43. Anon-transitory computer-readable medium storing instructions that, whenexecuted by one or more processors of a base station associated with afirst cell, cause the base station to: receive, from a wireless device,a first message comprising a measurement report based on one or moresecond cells; transmit, to a computing device, a second messagecomprising an indication of a handover of the wireless device to asecond cell of the one or more second cells; receive, from the computingdevice, a third message indicating a type of a random access procedurefor the handover, wherein the type of the random access procedurecomprises a two-step random access procedure or a four-step randomaccess procedure; and transmit, to the wireless device, a fourthmessage, associated with the handover, that comprises one or moreparameters indicating the type of the random access procedure for thehandover.
 44. The non-transitory computer-readable medium of claim 43,wherein: the computing device comprises a second base station associatedwith the second cell; and the second message comprises a handoverrequest.
 45. The non-transitory computer-readable medium of claim 43,wherein: the computing device comprises a core network device; and thesecond message indicates that the handover is requested.
 46. Thenon-transitory computer-readable medium of claim 43, wherein the one ormore parameters of the fourth message comprise, for the random accessprocedure, one or more of: a preamble identifier; or random accessresource information.
 47. The non-transitory computer-readable medium ofclaim 43, wherein the fourth message further comprises timing advanceinformation for transmission of one or more of a random access preambleor one or more transport blocks.
 48. The non-transitorycomputer-readable medium of claim 47, wherein the timing advanceinformation comprises one or more of: an indication of a zero timingadvance; or a value for a timing advance, wherein the value is estimatedby the base station or a computing device.
 49. A non-transitorycomputer-readable medium storing instructions that, when executed by oneor more processors of a computing device, cause the computing device to:receive, from a first base station associated with a first cell, a firstmessage comprising an indication for a handover of a wireless devicefrom the first cell to a second cell of one or more second cells; andtransmit, to the first base station and based on a determination toproceed with the handover, a second message that comprises one or moreparameters indicating a type of a random access procedure for thehandover, wherein the type of the random access procedure comprises atwo-step random access procedure or a four-step random access procedure.50. The non-transitory computer-readable medium of claim 49, wherein thesecond message comprises a handover request.
 51. The non-transitorycomputer-readable medium of claim 49, wherein the second messagecomprises an indication that the handover is required.
 52. Thenon-transitory computer-readable medium of claim 51, wherein theinstructions, when executed by the one or more processors, further causethe computing device to: transmit, to a second base station and based onthe first message, a third message comprising a handover request; andreceive, from the second base station, a fourth message comprising ahandover request acknowledgement that indicates the type of the randomaccess procedure for the handover.
 53. The non-transitorycomputer-readable medium of claim 52, wherein the fourth message isreceived based on a determination, by the second base station, that thehandover request is acceptable.
 54. The non-transitory computer-readablemedium of claim 49, wherein the computing device comprises at least oneof: a core network device; or a second base station associated with thesecond cell.
 55. A system comprising: a wireless device; and a firstbase station associated with a first cell, wherein the wireless devicecomprises: one or more processors; and memory storing instructions that,when executed by the one or more processors of the wireless device,cause the wireless device to: transmit, to the first base station, afirst message comprising a measurement report based on one or moresecond cells; receive, from the first base station, a second messagecomprising a command for a handover from the first cell to a second cellof the one or more second cells, wherein the second message comprisesone or more parameters indicating a type of a random access procedurefor the handover, and wherein the type of the random access procedurecomprises a two-step random access procedure or a four-step randomaccess procedure; and transmit, to a second base station associated withthe second cell, a random access preamble employing the type of therandom access procedure indicated in the second message, and wherein thefirst base station comprises: one or more processors; and memory storinginstructions that, when executed by the one or more processors of thefirst base station, cause the first base station to: receive, from thewireless device, the first message; transmit, to the second basestation, a third message comprising an indication of the handover;receive, from the second base station, a fourth message indicating thetype of the random access procedure for the handover; and transmit, tothe wireless device, the second message that comprises the one or moreparameters indicating the type of the random access procedure for thehandover.
 56. The system of claim 55, wherein the instructions stored inthe memory of the wireless device, when executed by the one or moreprocessors of the wireless device, further cause the wireless device to:transmit one or more transport blocks overlapping in time with therandom access preamble.
 57. The system of claim 55, wherein the one ormore parameters of the second message comprise, for the random accessprocedure, one or more of: a preamble identifier; or random accessresource information.
 58. The system of claim 55, wherein the secondmessage further comprises: timing advance information for transmissionof one or more of the random access preamble or one or more transportblocks.
 59. The system of claim 55, wherein the instructions stored inthe memory of the wireless device, when executed by the one or moreprocessors of the wireless device, further cause the wireless device to:transmit, in a first step of a four-step random access procedure, asecond random access preamble.
 60. The system of claim 55, wherein thesecond message comprises: random access channel configurationinformation for a two-step random access procedure; and radio resourceconfiguration parameters for the two-step random access procedure. 61.The system of claim 55, further comprising: the second base station,wherein the second base station comprises: one or more processors; andmemory storing instructions that, when executed by the one or moreprocessors of the second base station, cause the second base station to:receive, from the first base station, the third message comprising theindication of the handover; and transmit, to the first base station, thefourth message indicating the type of the random access procedure forthe handover.